fix: Add /api prefix to focus_areas router

- Changed prefix from '/focus-areas' to '/api/focus-areas'
- Consistent with all other routers (goals, prompts, etc.)
- Fixes 404 Not Found on /admin/focus-areas page

backend/routers/focus_areas.py

@@ -8,7 +8,7 @@ from typing import Optional, List
 from db import get_db, get_cursor, r2d
 from auth import require_auth
 
-router = APIRouter(prefix="/focus-areas", tags=["focus-areas"])
+router = APIRouter(prefix="/api/focus-areas", tags=["focus-areas"])
 
 # ============================================================================
 # Models