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/alembic/versions/0013_family_profile_planner_config.py

@@ -0,0 +1,28 @@
+"""Add planner_config JSONB to family_profile.
+
+Revision ID: 0013
+Revises: 0012
+Create Date: 2026-05-24 17:00:00
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision: str = "0013"
+down_revision: Union[str, None] = "0012"
+branch_labels: Union[Sequence[str], None] = None
+depends_on: Union[Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "family_profile",
+        sa.Column("planner_config", postgresql.JSONB, nullable=True),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("family_profile", "planner_config")