feat: add manual nutrition entry form with auto-detect

Features:
- Manual entry form above data list
- Date picker with auto-load existing entries
- Upsert logic: creates new or updates existing entry
- Smart button text: "Hinzufügen" vs "Aktualisieren"
- Prevents duplicate entries per day
- Feature enforcement for nutrition_entries

Backend:
- POST /nutrition - Create or update entry (upsert)
- GET /nutrition/by-date/{date} - Load entry by date
- Auto-detects existing entry and switches to UPDATE mode
- Increments usage counter only on INSERT

Frontend:
- EntryForm component with date picker + macros inputs
- Auto-loads data when date changes
- Shows info message when entry exists
- Success/error feedback
- Disabled state while loading/saving

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/routers/nutrition.py

@@ -99,6 +99,61 @@ async def import_nutrition_csv(file: UploadFile=File(...), x_profile_id: Optiona
             "date_range":{"from":min(days) if days else None,"to":max(days) if days else None}}
 
 
+@router.post("")
+def create_nutrition(date: str, kcal: float, protein_g: float, fat_g: float, carbs_g: float,
+                     x_profile_id: Optional[str]=Header(default=None), session: dict=Depends(require_auth)):
+    """Create or update nutrition entry for a specific date."""
+    pid = get_pid(x_profile_id)
+
+    # Validate date format
+    try:
+        datetime.strptime(date, '%Y-%m-%d')
+    except ValueError:
+        raise HTTPException(400, "Ungültiges Datumsformat. Erwartet: YYYY-MM-DD")
+
+    with get_db() as conn:
+        cur = get_cursor(conn)
+        # Check if entry exists
+        cur.execute("SELECT id FROM nutrition_log WHERE profile_id=%s AND date=%s", (pid, date))
+        existing = cur.fetchone()
+
+        if existing:
+            # UPDATE existing entry
+            cur.execute("""
+                UPDATE nutrition_log
+                SET kcal=%s, protein_g=%s, fat_g=%s, carbs_g=%s, source='manual'
+                WHERE id=%s AND profile_id=%s
+            """, (round(kcal,1), round(protein_g,1), round(fat_g,1), round(carbs_g,1), existing['id'], pid))
+            return {"success": True, "mode": "updated", "id": existing['id']}
+        else:
+            # Phase 4: Check feature access before INSERT
+            access = check_feature_access(pid, 'nutrition_entries')
+            log_feature_usage(pid, 'nutrition_entries', access, 'create')
+
+            if not access['allowed']:
+                logger.warning(
+                    f"[FEATURE-LIMIT] User {pid} blocked: "
+                    f"nutrition_entries {access['reason']} (used: {access['used']}, limit: {access['limit']})"
+                )
+                raise HTTPException(
+                    status_code=403,
+                    detail=f"Limit erreicht: Du hast das Kontingent für Ernährungseinträge überschritten ({access['used']}/{access['limit']}). "
+                           f"Bitte kontaktiere den Admin oder warte bis zum nächsten Reset."
+                )
+
+            # INSERT new entry
+            new_id = str(uuid.uuid4())
+            cur.execute("""
+                INSERT INTO nutrition_log (id, profile_id, date, kcal, protein_g, fat_g, carbs_g, source, created)
+                VALUES (%s, %s, %s, %s, %s, %s, %s, 'manual', CURRENT_TIMESTAMP)
+            """, (new_id, pid, date, round(kcal,1), round(protein_g,1), round(fat_g,1), round(carbs_g,1)))
+
+            # Phase 2: Increment usage counter
+            increment_feature_usage(pid, 'nutrition_entries')
+
+            return {"success": True, "mode": "created", "id": new_id}
+
+
 @router.get("")
 def list_nutrition(limit: int=365, x_profile_id: Optional[str]=Header(default=None), session: dict=Depends(require_auth)):
     """Get nutrition entries for current profile."""
@@ -110,6 +165,17 @@ def list_nutrition(limit: int=365, x_profile_id: Optional[str]=Header(default=No
         return [r2d(r) for r in cur.fetchall()]
 
 
+@router.get("/by-date/{date}")
+def get_nutrition_by_date(date: str, x_profile_id: Optional[str]=Header(default=None), session: dict=Depends(require_auth)):
+    """Get nutrition entry for a specific date."""
+    pid = get_pid(x_profile_id)
+    with get_db() as conn:
+        cur = get_cursor(conn)
+        cur.execute("SELECT * FROM nutrition_log WHERE profile_id=%s AND date=%s", (pid, date))
+        row = cur.fetchone()
+        return r2d(row) if row else None
+
+
 @router.get("/correlations")
 def nutrition_correlations(x_profile_id: Optional[str]=Header(default=None), session: dict=Depends(require_auth)):
     """Get nutrition data correlated with weight and body fat."""

frontend/src/pages/NutritionPage.jsx

@@ -18,6 +18,179 @@ function rollingAvg(arr, key, window=7) {
   })
 }
 
+// ── Entry Form (Create/Update) ───────────────────────────────────────────────
+function EntryForm({ onSaved }) {
+  const [date, setDate] = useState(dayjs().format('YYYY-MM-DD'))
+  const [values, setValues] = useState({ kcal: '', protein_g: '', fat_g: '', carbs_g: '' })
+  const [existingId, setExistingId] = useState(null)
+  const [loading, setLoading] = useState(false)
+  const [saving, setSaving] = useState(false)
+  const [error, setError] = useState(null)
+  const [success, setSuccess] = useState(null)
+
+  // Load data for selected date
+  useEffect(() => {
+    const load = async () => {
+      if (!date) return
+      setLoading(true)
+      setError(null)
+      try {
+        const data = await nutritionApi.getNutritionByDate(date)
+        if (data) {
+          setValues({
+            kcal: data.kcal || '',
+            protein_g: data.protein_g || '',
+            fat_g: data.fat_g || '',
+            carbs_g: data.carbs_g || ''
+          })
+          setExistingId(data.id)
+        } else {
+          setValues({ kcal: '', protein_g: '', fat_g: '', carbs_g: '' })
+          setExistingId(null)
+        }
+      } catch(e) {
+        console.error('Failed to load entry:', e)
+      } finally {
+        setLoading(false)
+      }
+    }
+    load()
+  }, [date])
+
+  const handleSave = async () => {
+    if (!date || !values.kcal) {
+      setError('Datum und Kalorien sind Pflichtfelder')
+      return
+    }
+
+    setSaving(true)
+    setError(null)
+    setSuccess(null)
+    try {
+      const result = await nutritionApi.createNutrition(
+        date,
+        parseFloat(values.kcal) || 0,
+        parseFloat(values.protein_g) || 0,
+        parseFloat(values.fat_g) || 0,
+        parseFloat(values.carbs_g) || 0
+      )
+      setSuccess(result.mode === 'created' ? 'Eintrag hinzugefügt' : 'Eintrag aktualisiert')
+      setTimeout(() => setSuccess(null), 3000)
+      onSaved()
+    } catch(e) {
+      if (e.message.includes('Limit erreicht')) {
+        setError(e.message)
+      } else {
+        setError('Speichern fehlgeschlagen: ' + e.message)
+      }
+      setTimeout(() => setError(null), 5000)
+    } finally {
+      setSaving(false)
+    }
+  }
+
+  return (
+    <div className="card section-gap">
+      <div className="card-title">Eintrag hinzufügen / bearbeiten</div>
+
+      {error && (
+        <div style={{padding:'8px 12px',background:'#FCEBEB',borderRadius:8,fontSize:13,color:'#D85A30',marginBottom:12}}>
+          {error}
+        </div>
+      )}
+      {success && (
+        <div style={{padding:'8px 12px',background:'var(--accent-light)',borderRadius:8,fontSize:13,color:'var(--accent-dark)',marginBottom:12}}>
+          ✓ {success}
+        </div>
+      )}
+
+      <div style={{display:'grid',gridTemplateColumns:'1fr 1fr',gap:12,marginBottom:12}}>
+        <div style={{gridColumn:'1 / -1'}}>
+          <label className="form-label">Datum</label>
+          <input
+            type="date"
+            className="form-input"
+            value={date}
+            onChange={e => setDate(e.target.value)}
+            max={dayjs().format('YYYY-MM-DD')}
+            style={{width:'100%'}}
+          />
+          {existingId && !loading && (
+            <div style={{fontSize:11,color:'var(--accent)',marginTop:4}}>
+              ℹ️ Eintrag existiert bereits – wird beim Speichern aktualisiert
+            </div>
+          )}
+        </div>
+
+        <div>
+          <label className="form-label">Kalorien *</label>
+          <input
+            type="number"
+            className="form-input"
+            value={values.kcal}
+            onChange={e => setValues({...values, kcal: e.target.value})}
+            placeholder="z.B. 2000"
+            disabled={loading}
+            style={{width:'100%'}}
+          />
+        </div>
+
+        <div>
+          <label className="form-label">Protein (g)</label>
+          <input
+            type="number"
+            className="form-input"
+            value={values.protein_g}
+            onChange={e => setValues({...values, protein_g: e.target.value})}
+            placeholder="z.B. 150"
+            disabled={loading}
+            style={{width:'100%'}}
+          />
+        </div>
+
+        <div>
+          <label className="form-label">Fett (g)</label>
+          <input
+            type="number"
+            className="form-input"
+            value={values.fat_g}
+            onChange={e => setValues({...values, fat_g: e.target.value})}
+            placeholder="z.B. 80"
+            disabled={loading}
+            style={{width:'100%'}}
+          />
+        </div>
+
+        <div>
+          <label className="form-label">Kohlenhydrate (g)</label>
+          <input
+            type="number"
+            className="form-input"
+            value={values.carbs_g}
+            onChange={e => setValues({...values, carbs_g: e.target.value})}
+            placeholder="z.B. 200"
+            disabled={loading}
+            style={{width:'100%'}}
+          />
+        </div>
+      </div>
+
+      <button
+        className="btn btn-primary btn-full"
+        onClick={handleSave}
+        disabled={saving || loading || !date || !values.kcal}>
+        {saving ? (
+          <><div className="spinner" style={{width:14,height:14}}/> Speichere…</>
+        ) : existingId ? (
+          '📝 Eintrag aktualisieren'
+        ) : (
+          '➕ Eintrag hinzufügen'
+        )}
+      </button>
+    </div>
+  )
+}
+
 // ── Data Tab (Editable Entry List) ───────────────────────────────────────────
 function DataTab({ entries, onUpdate }) {
   const [editId, setEditId] = useState(null)
@@ -619,7 +792,10 @@ export default function NutritionPage() {
           </div>
 
           {tab==='data' && (
-            <DataTab entries={entries} onUpdate={load}/>
+            <>
+              <EntryForm onSaved={load}/>
+              <DataTab entries={entries} onUpdate={load}/>
+            </>
           )}
 
           {tab==='overview' && (

frontend/src/utils/api.js

@@ -83,6 +83,8 @@ export const api = {
   nutritionCorrelations:  ()      => req('/nutrition/correlations'),
   nutritionWeekly:        (w=16)  => req(`/nutrition/weekly?weeks=${w}`),
   nutritionImportHistory: ()      => req('/nutrition/import-history'),
+  getNutritionByDate:     (date)  => req(`/nutrition/by-date/${date}`),
+  createNutrition:        (date,kcal,protein,fat,carbs) => req(`/nutrition?date=${date}&kcal=${kcal}&protein_g=${protein}&fat_g=${fat}&carbs_g=${carbs}`,{method:'POST'}),
   updateNutrition:        (id,kcal,protein,fat,carbs) => req(`/nutrition/${id}?kcal=${kcal}&protein_g=${protein}&fat_g=${fat}&carbs_g=${carbs}`,{method:'PUT'}),
   deleteNutrition:        (id)    => req(`/nutrition/${id}`,{method:'DELETE'}),