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/pages/toronto/callbacks/__init__.py

@@ -18,8 +18,7 @@ _CMHC_ZONES_PATH = Path("data/toronto/raw/geo/cmhc_zones.geojson")
 _cmhc_parser = CMHCZoneParser(_CMHC_ZONES_PATH) if _CMHC_ZONES_PATH.exists() else None
 CMHC_ZONES_GEOJSON = _cmhc_parser.get_geojson_for_choropleth() if _cmhc_parser else None
 
-# Load Toronto neighbourhoods GeoJSON for purchase choropleth maps
-# Note: This is a temporary proxy until TRREB district boundaries are digitized
+# Load Toronto neighbourhoods GeoJSON for choropleth maps
 _NEIGHBOURHOODS_PATH = Path("data/toronto/raw/geo/toronto_neighbourhoods.geojson")
 _neighbourhood_parser = (
     NeighbourhoodParser(_NEIGHBOURHOODS_PATH) if _NEIGHBOURHOODS_PATH.exists() else None
@@ -30,9 +29,7 @@ NEIGHBOURHOODS_GEOJSON = (
     else None
 )
 
-# Sample purchase data for all 158 City of Toronto neighbourhoods
-# Note: This is SAMPLE DATA until TRREB district boundaries are digitized (Issue #25)
-# Once TRREB boundaries are available, this will be replaced with real TRREB data by district
+# Sample data for all 158 City of Toronto neighbourhoods
 SAMPLE_PURCHASE_DATA = [
     {
         "neighbourhood_id": 1,
@@ -1486,11 +1483,7 @@ SAMPLE_TIME_SERIES_DATA = [
     Input("toronto-year-selector", "value"),
 )
 def update_purchase_choropleth(metric: str, year: str) -> go.Figure:
-    """Update the purchase market choropleth map.
-
-    Note: Currently using City of Toronto neighbourhoods as a proxy.
-    Will switch to TRREB districts when boundaries are digitized.
-    """
+    """Update the neighbourhood choropleth map."""
     return create_choropleth_figure(
         geojson=NEIGHBOURHOODS_GEOJSON,
         data=SAMPLE_PURCHASE_DATA,