fix: focus areas slider NaN values and validation

Fixed multiple issues with relative weight sliders:
1. Sanitize focusData on load (ensure all 6 fields are numeric)
2. Sync focusTemp when clicking "Anpassen" button
3. Robust sum calculation filtering only *_pct fields
4. Convert NaN/undefined to 0 in all calculations
5. Safe Number() coercion before normalization

Fixes errors:
- "Gewichtung gesamt: NaN"
- "Input should be a valid integer, input: null"
- Prozent always showing 0%

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

frontend/src/pages/GoalsPage.jsx

@@ -92,8 +92,21 @@ export default function GoalsPage() {
       ])
       setGoalMode(modeData.goal_mode)
       setGoals(goalsData)
-      setFocusAreas(focusData)
-      setFocusTemp(focusData) // Initialize temp state
+
+      // Ensure all focus fields are present and numeric
+      const sanitizedFocus = {
+        weight_loss_pct: focusData?.weight_loss_pct ?? 0,
+        muscle_gain_pct: focusData?.muscle_gain_pct ?? 0,
+        strength_pct: focusData?.strength_pct ?? 0,
+        endurance_pct: focusData?.endurance_pct ?? 0,
+        flexibility_pct: focusData?.flexibility_pct ?? 0,
+        health_pct: focusData?.health_pct ?? 0,
+        custom: focusData?.custom,
+        updated_at: focusData?.updated_at
+      }
+
+      setFocusAreas(sanitizedFocus)
+      setFocusTemp(sanitizedFocus)
 
       // Convert types array to map for quick lookup
       const typesMap = {}
@@ -278,7 +291,10 @@ export default function GoalsPage() {
           {!focusEditing && focusAreas && (
             <button
               className="btn-secondary"
-              onClick={() => setFocusEditing(true)}
+              onClick={() => {
+                setFocusTemp(focusAreas) // Sync temp state before editing
+                setFocusEditing(true)
+              }}
               style={{ padding: '6px 12px' }}
             >
               <Pencil size={14} /> Anpassen
@@ -306,9 +322,12 @@ export default function GoalsPage() {
                 { key: 'flexibility_pct', label: 'Beweglichkeit', icon: '🤸', color: '#E67E22' },
                 { key: 'health_pct', label: 'Gesundheit', icon: '❤️', color: '#F59E0B' }
               ].map(area => {
-                const weight = Math.round(focusTemp[area.key] / 10)
-                const sum = Object.values(focusTemp).reduce((a, b) => a + b, 0)
-                const actualPercent = sum > 0 ? Math.round(focusTemp[area.key] / sum * 100) : 0
+                const rawValue = Number(focusTemp[area.key]) || 0
+                const weight = Math.round(rawValue / 10)
+                const sum = Object.entries(focusTemp)
+                  .filter(([k]) => k.endsWith('_pct'))
+                  .reduce((acc, [k, v]) => acc + (Number(v) || 0), 0)
+                const actualPercent = sum > 0 ? Math.round(rawValue / sum * 100) : 0
 
                 return (
                   <div key={area.key}>
@@ -361,7 +380,12 @@ export default function GoalsPage() {
                   Gewichtung gesamt:
                 </span>
                 <span style={{ fontSize: 18, fontWeight: 600, color: 'var(--text1)' }}>
-                  {Object.values(focusTemp).reduce((a, b) => a + b, 0) / 10}
+                  {(() => {
+                    const total = Object.entries(focusTemp)
+                      .filter(([k]) => k.endsWith('_pct'))
+                      .reduce((acc, [k, v]) => acc + (Number(v) || 0), 0)
+                    return (total / 10).toFixed(1)
+                  })()}
                 </span>
               </div>
               <div style={{ fontSize: 12, marginTop: 4, color: 'var(--text3)' }}>
@@ -374,18 +398,25 @@ export default function GoalsPage() {
               <button
                 className="btn-primary"
                 onClick={async () => {
-                  const sum = Object.values(focusTemp).reduce((a, b) => a + b, 0)
+                  // Calculate sum (filter out NaN/undefined)
+                  const sum = Object.entries(focusTemp)
+                    .filter(([k]) => k.endsWith('_pct'))
+                    .reduce((acc, [k, v]) => acc + (Number(v) || 0), 0)
 
-                  if (sum === 0) {
+                  if (sum === 0 || isNaN(sum)) {
                     setError('Mindestens ein Bereich muss gewichtet sein')
                     return
                   }
 
-                  // Normalize to percentages
-                  const normalized = {}
-                  Object.keys(focusTemp).forEach(key => {
-                    normalized[key] = Math.round(focusTemp[key] / sum * 100)
-                  })
+                  // Normalize to percentages (ensure no NaN values)
+                  const normalized = {
+                    weight_loss_pct: Math.round((Number(focusTemp.weight_loss_pct) || 0) / sum * 100),
+                    muscle_gain_pct: Math.round((Number(focusTemp.muscle_gain_pct) || 0) / sum * 100),
+                    strength_pct: Math.round((Number(focusTemp.strength_pct) || 0) / sum * 100),
+                    endurance_pct: Math.round((Number(focusTemp.endurance_pct) || 0) / sum * 100),
+                    flexibility_pct: Math.round((Number(focusTemp.flexibility_pct) || 0) / sum * 100),
+                    health_pct: Math.round((Number(focusTemp.health_pct) || 0) / sum * 100)
+                  }
 
                   // Ensure sum is exactly 100 (adjust largest value if needed due to rounding)
                   const normalizedSum = Object.values(normalized).reduce((a, b) => a + b, 0)