feat: add GeoJSON parsers and choropleth map visualization

- Add geo.py parser module with CMHCZoneParser, TRREBDistrictParser,
  and NeighbourhoodParser for loading geographic boundaries
- Add coordinate reprojection support (EPSG:3857 to WGS84)
- Organize geo data in data/toronto/raw/geo/ directory
- Add CMHC zones GeoJSON (31 zones) for rental market choropleth
- Add Toronto neighbourhoods GeoJSON (158) as purchase market proxy
- Update callbacks with real CMHC 2024 rental data
- Add sample purchase data for all 158 neighbourhoods
- Update pre-commit config to exclude geo data files

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

tests/test_placeholder.py

@@ -0,0 +1,6 @@
+"""Placeholder test to ensure pytest collection succeeds."""
+
+
+def test_placeholder():
+    """Remove this once real tests are added."""
+    assert True