fix: [BUG-003] correlations chart shows all weight data with extrapolation

Changes:
- Show all data points (kcal OR weight, not only both)
- Extrapolate missing kcal values at end (use last known value)
- Dashed lines (strokeDasharray) for extrapolated values
- Solid lines for real measurements
- Weight always interpolates gaps (connectNulls=true)

Visual distinction:
- Solid = Real measurements + gap interpolation
- Dashed = Extrapolation at chart end

Closes: BUG-003

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

frontend/src/pages/NutritionPage.jsx

@@ -598,26 +598,62 @@ function OverviewCards({ data }) {
 
 // ── Chart: Kalorien vs Gewicht ────────────────────────────────────────────────
 function CaloriesVsWeight({ data }) {
-  const filtered = data.filter(d => d.kcal && d.weight)
-  const withAvg  = rollingAvg(filtered.map(d=>({...d,date:dayjs(d.date).format('DD.MM')})), 'kcal')
+  // BUG-003 fix: Show all weight data, extrapolate kcal if missing
+  const filtered = data.filter(d => d.kcal || d.weight)
   if (filtered.length < 3) return (
     <div style={{padding:20,textAlign:'center',color:'var(--text3)',fontSize:13}}>
-      Zu wenig gemeinsame Daten (Gewicht + Kalorien am selben Tag nötig)
+      Zu wenig Daten für diese Auswertung
     </div>
   )
+
+  // Find last real kcal value
+  const lastKcalIndex = filtered.findLastIndex(d => d.kcal)
+  const lastKcal = lastKcalIndex >= 0 ? filtered[lastKcalIndex].kcal : null
+
+  // Extrapolate missing kcal values at the end
+  const withExtrapolated = filtered.map((d, i) => ({
+    ...d,
+    kcal: d.kcal || (i > lastKcalIndex && lastKcal ? lastKcal : null),
+    isKcalExtrapolated: !d.kcal && i > lastKcalIndex && lastKcal
+  }))
+
+  // Format dates and calculate rolling average
+  const formatted = withExtrapolated.map(d => ({
+    ...d,
+    date: dayjs(d.date).format('DD.MM')
+  }))
+  const withAvg = rollingAvg(formatted, 'kcal')
+
+  // Split into real and extrapolated segments for dashed lines
+  const realData = withAvg.map(d => ({
+    ...d,
+    kcal_extrap: d.isKcalExtrapolated ? d.kcal : null,
+    kcal_avg_extrap: d.isKcalExtrapolated ? d.kcal_avg : null,
+    kcal: d.isKcalExtrapolated ? null : d.kcal,
+    kcal_avg: d.isKcalExtrapolated ? null : d.kcal_avg
+  }))
+
   return (
     <ResponsiveContainer width="100%" height={220}>
-      <LineChart data={withAvg} margin={{top:4,right:8,bottom:0,left:-16}}>
+      <LineChart data={realData} margin={{top:4,right:8,bottom:0,left:-16}}>
         <CartesianGrid stroke="var(--border)" strokeDasharray="3 3"/>
         <XAxis dataKey="date" tick={{fontSize:9,fill:'var(--text3)'}} tickLine={false}
-          interval={Math.max(0,Math.floor(withAvg.length/6)-1)}/>
+          interval={Math.max(0,Math.floor(realData.length/6)-1)}/>
         <YAxis yAxisId="kcal" tick={{fontSize:9,fill:'var(--text3)'}} tickLine={false} domain={['auto','auto']}/>
         <YAxis yAxisId="weight" orientation="right" tick={{fontSize:9,fill:'var(--text3)'}} tickLine={false} domain={['auto','auto']}/>
         <Tooltip contentStyle={{background:'var(--surface)',border:'1px solid var(--border)',borderRadius:8,fontSize:11}}
-          formatter={(v,n)=>[`${Math.round(v)} ${n==='weight'?'kg':'kcal'}`, n==='kcal_avg'?'Ø 7T Kalorien':n==='weight'?'Gewicht':'Kalorien']}/>
-        <Line yAxisId="kcal"   type="monotone" dataKey="kcal"     stroke="#EF9F2744" strokeWidth={1} dot={false}/>
-        <Line yAxisId="kcal"   type="monotone" dataKey="kcal_avg" stroke="#EF9F27"   strokeWidth={2} dot={false} name="kcal_avg"/>
-        <Line yAxisId="weight" type="monotone" dataKey="weight"   stroke="#378ADD"   strokeWidth={2} dot={{r:3,fill:'#378ADD'}} name="weight"/>
+          formatter={(v,n)=>[`${Math.round(v)} ${n==='weight'?'kg':'kcal'}`, n.includes('avg')?'Ø 7T Kalorien':n==='weight'?'Gewicht':'Kalorien']}/>
+
+        {/* Real kcal values - solid lines */}
+        <Line yAxisId="kcal" type="monotone" dataKey="kcal" stroke="#EF9F2744" strokeWidth={1} dot={false} connectNulls={false}/>
+        <Line yAxisId="kcal" type="monotone" dataKey="kcal_avg" stroke="#EF9F27" strokeWidth={2} dot={false} name="kcal_avg" connectNulls={false}/>
+
+        {/* Extrapolated kcal values - dashed lines */}
+        <Line yAxisId="kcal" type="monotone" dataKey="kcal_extrap" stroke="#EF9F2744" strokeWidth={1} strokeDasharray="3 3" dot={false} connectNulls={false}/>
+        <Line yAxisId="kcal" type="monotone" dataKey="kcal_avg_extrap" stroke="#EF9F27" strokeWidth={2} strokeDasharray="3 3" dot={false} connectNulls={false}/>
+
+        {/* Weight - always solid */}
+        <Line yAxisId="weight" type="monotone" dataKey="weight" stroke="#378ADD" strokeWidth={2} dot={{r:3,fill:'#378ADD'}} name="weight" connectNulls={true}/>
       </LineChart>
     </ResponsiveContainer>
   )