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/schemas/dimensions.py

@@ -41,15 +41,6 @@ class Confidence(str, Enum):
     LOW = "low"
 
 
-class AreaType(str, Enum):
-    """TRREB area type."""
-
-    WEST = "West"
-    CENTRAL = "Central"
-    EAST = "East"
-    NORTH = "North"
-
-
 class TimeDimension(BaseModel):
     """Schema for time dimension record."""
 
@@ -62,15 +53,6 @@ class TimeDimension(BaseModel):
     is_month_start: bool = True
 
 
-class TRREBDistrict(BaseModel):
-    """Schema for TRREB district dimension."""
-
-    district_code: str = Field(max_length=3, description="W01, C01, E01, etc.")
-    district_name: str = Field(max_length=100)
-    area_type: AreaType
-    geometry_wkt: str | None = Field(default=None, description="WKT geometry string")
-
-
 class CMHCZone(BaseModel):
     """Schema for CMHC zone dimension."""