feat: auto-assign goal category based on goal type

Added intelligent category assignment:
- Weight, body_fat, lean_mass → Körper
- Strength, flexibility → Training
- BP, VO2Max, RHR, HRV → Gesundheit
- Sleep goals → Erholung
- Nutrition goals → Ernährung
- Unknown types → Sonstiges

Changes:
1. getCategoryForGoalType() mapping function
2. Auto-set category in handleGoalTypeChange()
3. Auto-set category in handleCreateGoal()

User can still manually change category if needed.

Fixes: Blood pressure goals wrongly categorized as 'Training'

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

frontend/src/pages/GoalsPage.jsx

@@ -22,6 +22,39 @@ const PRIORITY_LEVELS = {
   3: { label: 'Niedrig', stars: '⭐', color: '#CBD5E1' }
 }
 
+// Auto-assign category based on goal_type
+const getCategoryForGoalType = (goalType) => {
+  const mapping = {
+    // Body composition
+    'weight': 'body',
+    'body_fat': 'body',
+    'lean_mass': 'body',
+
+    // Training
+    'strength': 'training',
+    'flexibility': 'training',
+    'training_frequency': 'training',
+
+    // Health/Vitals
+    'vo2max': 'health',
+    'rhr': 'health',
+    'bp': 'health',
+    'hrv': 'health',
+
+    // Recovery
+    'sleep_quality': 'recovery',
+    'sleep_duration': 'recovery',
+    'rest_days': 'recovery',
+
+    // Nutrition
+    'calories': 'nutrition',
+    'protein': 'nutrition',
+    'healthy_eating': 'nutrition'
+  }
+
+  return mapping[goalType] || 'other'
+}
+
 export default function GoalsPage() {
   const [goalMode, setGoalMode] = useState(null)
   const [focusAreas, setFocusAreas] = useState(null)
@@ -141,7 +174,7 @@ export default function GoalsPage() {
     setFormData({
       goal_type: firstType,
       is_primary: goals.length === 0, // First goal is primary by default
-      category: 'body',
+      category: getCategoryForGoalType(firstType),  // Auto-assign based on type
       priority: 2,
       target_value: '',
       unit: goalTypesMap[firstType]?.unit || 'kg',
@@ -172,7 +205,8 @@ export default function GoalsPage() {
     setFormData(f => ({
       ...f,
       goal_type: type,
-      unit: goalTypesMap[type]?.unit || 'unit'
+      unit: goalTypesMap[type]?.unit || 'unit',
+      category: getCategoryForGoalType(type)  // Auto-assign category
     }))
   }