chore: Remove TRREB references from Python modules

- Remove DimTRREBDistrict model and FactPurchases model
- Remove TRREBDistrict schema and AreaType enum
- Remove TRREBDistrictParser from geo parsers
- Remove load_trreb_districts from dimension loaders
- Remove create_district_map from choropleth figures
- Remove get_demo_districts and get_demo_purchase_data from demo_data
- Update summary metrics to remove purchase-related metrics
- Update callbacks to remove TRREB-related comments
- Update methodology page to remove TRREB data source section
- Update dashboard data notice to remove TRREB mention

Closes #49

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

portfolio_app/toronto/models/dimensions.py

@@ -23,20 +23,6 @@ class DimTime(Base):
     is_month_start: Mapped[bool] = mapped_column(Boolean, default=True)
 
 
-class DimTRREBDistrict(Base):
-    """TRREB district dimension table with PostGIS geometry."""
-
-    __tablename__ = "dim_trreb_district"
-
-    district_key: Mapped[int] = mapped_column(
-        Integer, primary_key=True, autoincrement=True
-    )
-    district_code: Mapped[str] = mapped_column(String(3), nullable=False, unique=True)
-    district_name: Mapped[str] = mapped_column(String(100), nullable=False)
-    area_type: Mapped[str] = mapped_column(String(10), nullable=False)
-    geometry = mapped_column(Geometry("POLYGON", srid=4326), nullable=True)
-
-
 class DimCMHCZone(Base):
     """CMHC zone dimension table with PostGIS geometry."""