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/loaders/dimensions.py

@@ -9,13 +9,11 @@ from portfolio_app.toronto.models import (
     DimNeighbourhood,
     DimPolicyEvent,
     DimTime,
-    DimTRREBDistrict,
 )
 from portfolio_app.toronto.schemas import (
     CMHCZone,
     Neighbourhood,
     PolicyEvent,
-    TRREBDistrict,
 )
 
 from .base import get_session, upsert_by_key
@@ -97,42 +95,6 @@ def load_time_dimension(
         return _load(sess)
 
 
-def load_trreb_districts(
-    districts: list[TRREBDistrict],
-    session: Session | None = None,
-) -> int:
-    """Load TRREB district dimension.
-
-    Args:
-        districts: List of validated district schemas.
-        session: Optional existing session.
-
-    Returns:
-        Number of records loaded.
-    """
-
-    def _load(sess: Session) -> int:
-        records = []
-        for d in districts:
-            dim = DimTRREBDistrict(
-                district_code=d.district_code,
-                district_name=d.district_name,
-                area_type=d.area_type.value,
-                geometry=d.geometry_wkt,
-            )
-            records.append(dim)
-
-        inserted, updated = upsert_by_key(
-            sess, DimTRREBDistrict, records, ["district_code"]
-        )
-        return inserted + updated
-
-    if session:
-        return _load(session)
-    with get_session() as sess:
-        return _load(sess)
-
-
 def load_cmhc_zones(
     zones: list[CMHCZone],
     session: Session | None = None,