feat: add GET /api/features/usage endpoint (Phase 3)

- Add user-facing usage overview endpoint
- Returns all features with usage, limits, reset info
- Fully dynamic - automatically includes new features
- Phase 3: Frontend Display preparation

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

backend/routers/features.py

@@ -2,11 +2,16 @@
 Feature Management Endpoints for Mitai Jinkendo
 
 Admin-only CRUD for features registry.
+User endpoint for feature usage overview (Phase 3).
 """
-from fastapi import APIRouter, HTTPException, Depends
+from typing import Optional
+from datetime import datetime
+
+from fastapi import APIRouter, HTTPException, Header, Depends
 
 from db import get_db, get_cursor, r2d
 from auth import require_admin, require_auth, check_feature_access
+from routers.profiles import get_pid
 
 router = APIRouter(prefix="/api/features", tags=["features"])
 
@@ -136,3 +141,82 @@ def check_access(feature_id: str, session: dict = Depends(require_auth)):
     profile_id = session['profile_id']
     result = check_feature_access(profile_id, feature_id)
     return result
+
+
+@router.get("/usage")
+def get_feature_usage(x_profile_id: Optional[str]=Header(default=None), session: dict=Depends(require_auth)):
+    """
+    User: Get usage overview for all active features (Phase 3: Frontend Display).
+
+    Returns list of all features with current usage, limits, and reset info.
+    Automatically includes new features from database - no code changes needed.
+
+    Response:
+        [
+            {
+                "feature_id": "weight_entries",
+                "name": "Gewichtseinträge",
+                "description": "Anzahl der Gewichtseinträge",
+                "category": "data",
+                "limit_type": "count",
+                "reset_period": "never",
+                "used": 5,
+                "limit": 10,
+                "remaining": 5,
+                "allowed": true,
+                "reset_at": null
+            },
+            ...
+        ]
+    """
+    pid = get_pid(x_profile_id)
+
+    with get_db() as conn:
+        cur = get_cursor(conn)
+
+        # Get all active features (dynamic - picks up new features automatically)
+        cur.execute("""
+            SELECT id, name, description, category, limit_type, reset_period
+            FROM features
+            WHERE active = true
+            ORDER BY category, name
+        """)
+        features = [r2d(r) for r in cur.fetchall()]
+
+        result = []
+        for feature in features:
+            # Use existing check_feature_access to get usage and limits
+            # This respects user overrides, tier limits, and feature defaults
+            access = check_feature_access(pid, feature['id'])
+
+            # Get reset date from user_feature_usage
+            cur.execute("""
+                SELECT reset_at
+                FROM user_feature_usage
+                WHERE profile_id = %s AND feature_id = %s
+            """, (pid, feature['id']))
+            usage_row = cur.fetchone()
+
+            # Format reset_at as ISO string
+            reset_at = None
+            if usage_row and usage_row['reset_at']:
+                if isinstance(usage_row['reset_at'], datetime):
+                    reset_at = usage_row['reset_at'].isoformat()
+                else:
+                    reset_at = str(usage_row['reset_at'])
+
+            result.append({
+                'feature_id': feature['id'],
+                'name': feature['name'],
+                'description': feature.get('description'),
+                'category': feature.get('category'),
+                'limit_type': feature['limit_type'],
+                'reset_period': feature['reset_period'],
+                'used': access['used'],
+                'limit': access['limit'],
+                'remaining': access['remaining'],
+                'allowed': access['allowed'],
+                'reset_at': reset_at
+            })
+
+        return result