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/facts.py

@@ -6,37 +6,6 @@ from sqlalchemy.orm import Mapped, mapped_column, relationship
 from .base import Base
 
 
-class FactPurchases(Base):
-    """Fact table for TRREB purchase/sales data.
-
-    Grain: One row per district per month.
-    """
-
-    __tablename__ = "fact_purchases"
-
-    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
-    date_key: Mapped[int] = mapped_column(
-        Integer, ForeignKey("dim_time.date_key"), nullable=False
-    )
-    district_key: Mapped[int] = mapped_column(
-        Integer, ForeignKey("dim_trreb_district.district_key"), nullable=False
-    )
-    sales_count: Mapped[int] = mapped_column(Integer, nullable=False)
-    dollar_volume: Mapped[float] = mapped_column(Numeric(15, 2), nullable=False)
-    avg_price: Mapped[float] = mapped_column(Numeric(12, 2), nullable=False)
-    median_price: Mapped[float] = mapped_column(Numeric(12, 2), nullable=False)
-    new_listings: Mapped[int] = mapped_column(Integer, nullable=False)
-    active_listings: Mapped[int] = mapped_column(Integer, nullable=False)
-    avg_dom: Mapped[int] = mapped_column(Integer, nullable=False)  # Days on market
-    avg_sp_lp: Mapped[float] = mapped_column(
-        Numeric(5, 2), nullable=False
-    )  # Sale/List ratio
-
-    # Relationships
-    time = relationship("DimTime", backref="purchases")
-    district = relationship("DimTRREBDistrict", backref="purchases")
-
-
 class FactRentals(Base):
     """Fact table for CMHC rental market data.