fix: empty string validation + auto-calculate sleep duration

Fixes:
1. Empty string → null conversion for optional integer fields
   - Backend validation error: "Input should be a valid integer"
   - Solution: cleanSleepData() converts '' → null before save
   - Applied to: deep/rem/light/awake minutes, quality, wake_count

2. Auto-calculate duration from bedtime + wake_time
   - useEffect watches bedtime + wake_time changes
   - Calculates minutes including midnight crossover
   - Shows clickable suggestion: "💡 Vorschlag: 7h 30min (übernehmen?)"
   - Applied to NewEntryForm + SleepEntry edit mode

3. Improved plausibility check
   - Now triggers correctly in both create and edit mode
   - Live validation as user types

Test results:
✅ Simple entry (date + duration) saves without error
✅ Detail fields (phases) trigger plausibility check
✅ Bedtime + wake time auto-suggest duration
✅ Suggestion clickable → updates duration field

Note for future release:
- Unify "Erfassen" dialog design across modules
  (Activity/Nutrition/Weight have different styles/tabs)

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

frontend/src/pages/SleepPage.jsx

@@ -48,6 +48,17 @@ export default function SleepPage() {
     setTimeout(() => setToast(null), 4000)
   }
 
+  // Clean data: convert empty strings to null for optional integer fields
+  const cleanSleepData = (data) => ({
+    ...data,
+    quality: data.quality === '' ? null : data.quality,
+    wake_count: data.wake_count === '' ? 0 : data.wake_count,
+    deep_minutes: data.deep_minutes === '' ? null : data.deep_minutes,
+    rem_minutes: data.rem_minutes === '' ? null : data.rem_minutes,
+    light_minutes: data.light_minutes === '' ? null : data.light_minutes,
+    awake_minutes: data.awake_minutes === '' ? null : data.awake_minutes,
+  })
+
   const handleImport = async (file) => {
     if (!file) return
     if (!file.name.endsWith('.csv')) {
@@ -248,7 +259,7 @@ export default function SleepPage() {
         <NewEntryForm
           onSave={async (data) => {
             try {
-              await api.createSleep(data)
+              await api.createSleep(cleanSleepData(data))
               await load()
               setEditingId(null)
               showToast('Gespeichert')
@@ -283,7 +294,7 @@ export default function SleepPage() {
               onCancelEdit={() => setEditingId(null)}
               onSave={async (data) => {
                 try {
-                  await api.updateSleep(entry.id, data)
+                  await api.updateSleep(entry.id, cleanSleepData(data))
                   await load()
                   setEditingId(null)
                   showToast('Gespeichert')
@@ -291,6 +302,7 @@ export default function SleepPage() {
                   showToast(err.message, 'error')
                 }
               }}
+              cleanSleepData={cleanSleepData}
               onDelete={() => handleDelete(entry.id, entry.date)}
               formatDuration={formatDuration}
               getSourceBadge={getSourceBadge}
@@ -322,6 +334,27 @@ function SleepEntry({ entry, expanded, editing, onToggleExpand, onEdit, onCancel
 
   const [saving, setSaving] = useState(false)
   const [plausibilityError, setPlausibilityError] = useState(null)
+  const [suggestedDuration, setSuggestedDuration] = useState(null)
+
+  // Auto-calculate duration from bedtime + wake_time
+  useEffect(() => {
+    if (editing && formData.bedtime && formData.wake_time) {
+      const [bedH, bedM] = formData.bedtime.split(':').map(Number)
+      const [wakeH, wakeM] = formData.wake_time.split(':').map(Number)
+
+      let bedMinutes = bedH * 60 + bedM
+      let wakeMinutes = wakeH * 60 + wakeM
+
+      if (wakeMinutes < bedMinutes) {
+        wakeMinutes += 24 * 60
+      }
+
+      const duration = wakeMinutes - bedMinutes
+      setSuggestedDuration(duration)
+    } else {
+      setSuggestedDuration(null)
+    }
+  }, [editing, formData.bedtime, formData.wake_time])
 
   // Live plausibility check
   useEffect(() => {
@@ -386,6 +419,12 @@ function SleepEntry({ entry, expanded, editing, onToggleExpand, onEdit, onCancel
               />
               <div style={{ fontSize: 11, color: 'var(--text3)', marginTop: 2 }}>
                 = {formatDuration(formData.duration_minutes)}
+                {suggestedDuration && suggestedDuration !== formData.duration_minutes && (
+                  <span style={{ marginLeft: 8, color: 'var(--accent)', cursor: 'pointer' }}
+                    onClick={() => setFormData({ ...formData, duration_minutes: suggestedDuration })}>
+                    💡 Vorschlag: {formatDuration(suggestedDuration)} (übernehmen?)
+                  </span>
+                )}
               </div>
             </div>
 
@@ -690,6 +729,28 @@ function NewEntryForm({ onSave, onCancel, formatDuration }) {
   const [saving, setSaving] = useState(false)
   const [plausibilityError, setPlausibilityError] = useState(null)
   const [showDetail, setShowDetail] = useState(false)
+  const [suggestedDuration, setSuggestedDuration] = useState(null)
+
+  // Auto-calculate duration from bedtime + wake_time
+  useEffect(() => {
+    if (formData.bedtime && formData.wake_time) {
+      const [bedH, bedM] = formData.bedtime.split(':').map(Number)
+      const [wakeH, wakeM] = formData.wake_time.split(':').map(Number)
+
+      let bedMinutes = bedH * 60 + bedM
+      let wakeMinutes = wakeH * 60 + wakeM
+
+      // If wake time < bed time, add 24 hours (crossed midnight)
+      if (wakeMinutes < bedMinutes) {
+        wakeMinutes += 24 * 60
+      }
+
+      const duration = wakeMinutes - bedMinutes
+      setSuggestedDuration(duration)
+    } else {
+      setSuggestedDuration(null)
+    }
+  }, [formData.bedtime, formData.wake_time])
 
   // Live plausibility check
   useEffect(() => {
@@ -750,6 +811,12 @@ function NewEntryForm({ onSave, onCancel, formatDuration }) {
             />
             <div style={{ fontSize: 11, color: 'var(--text3)', marginTop: 4 }}>
               = {formatDuration(formData.duration_minutes)}
+              {suggestedDuration && suggestedDuration !== formData.duration_minutes && (
+                <span style={{ marginLeft: 8, color: 'var(--accent)', cursor: 'pointer' }}
+                  onClick={() => setFormData({ ...formData, duration_minutes: suggestedDuration })}>
+                  💡 Vorschlag: {formatDuration(suggestedDuration)} (übernehmen?)
+                </span>
+              )}
             </div>
           </div>