fix: add missing start_date and reached_date to grouped goals query

Root cause: listGoalsGrouped() SELECT was missing g.start_date and g.reached_date
Result: Frontend used grouped goals for editing, so start_date was undefined

This is why target_date worked (it was in SELECT) but start_date didn't.

backend/routers/goals.py

@@ -663,7 +663,8 @@ def get_goals_grouped(session: dict = Depends(require_auth)):
         cur.execute("""
             SELECT
                 g.id, g.goal_type, g.target_value, g.current_value, g.start_value,
-                g.unit, g.target_date, g.status, g.is_primary, g.category, g.priority,
+                g.unit, g.start_date, g.target_date, g.reached_date, g.status,
+                g.is_primary, g.category, g.priority,
                 g.name, g.description, g.progress_pct, g.on_track, g.projection_date,
                 g.created_at, g.updated_at,
                 gt.label_de, gt.icon, gt.category as type_category,