feat(backend): tunable planner weights via family profile config

- Add planner_config JSONB to family_profile model + migration
- Add PlannerConfig.merge(overrides) + to_dict() for family-level override merging
- generate_meal_plan merges family.planner_config into DEFAULT before filtering/scoring/selection
- New endpoints on /api/profile:
  - GET /planner-config — returns merged effective config
  - PUT /planner-config — partial override validation + merge
  - DELETE /planner-config — reset to system defaults
- Schemas: PlannerConfigOverride, PlannerConfigResponse, PlannerConfigUpdateRequest
  with weight-sum validation (0.999–1.001)
- Export RecipeBase/Create/Read/Update from schemas/__init__ to resolve forward refs

backend/app/models/__init__.py

@@ -97,6 +97,7 @@ class FamilyProfile(Base):
     budget_per_meal = Column(Numeric(10, 2), default=50.00)
     calorie_target = Column(Integer)
     pending_approval_policy = Column(String(10), nullable=False, server_default="approve")
+    planner_config = Column(JSONB, nullable=True)
     created_at = Column(DateTime(timezone=True), server_default=func.now())
     updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())