feat(backend): persist plan scores on MealPlanItem

- Migration 0012 adds score (float) and components (jsonb) to meal_plan_item
- generate.py: populates score and components at create time
- schemas/MealPlanItemResponse: include score + components fields
- GET /api/meal-plans/{id}: returns persisted values instead of zeros

backend/app/models/__init__.py

@@ -1,5 +1,5 @@
 from sqlalchemy import (
-    Column, String, Integer, Numeric, Text, Boolean, Date, DateTime,
+    Column, String, Integer, Numeric, Float, Text, Boolean, Date, DateTime,
     ForeignKey, CheckConstraint, UniqueConstraint, Enum as SQLEnum
 )
 from sqlalchemy.dialects.postgresql import UUID, JSONB, ARRAY
@@ -228,6 +228,8 @@ class MealPlanItem(Base):
     denial_reason = Column(SQLEnum(DenialReason, name="denial_reason_enum", create_type=False, values_callable=lambda obj: [e.value for e in obj]))
     denial_details = Column(Text)
     estimated_cost = Column(Numeric(10, 2))
+    score = Column(Float)
+    components = Column(JSONB)
     used_pantry_items = Column(ARRAY(UUID(as_uuid=True)))
     created_at = Column(DateTime(timezone=True), server_default=func.now())
     updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())