fix: Complete seed script with all missing data + add statsmodels

- Seed script now seeds: amenities, population, median_age, census
  housing columns, housing mart (rent/affordability), overview mart
  (safety_score, population)
- Add statsmodels dependency for scatter plot trendlines
- Add dbt/.user.yml to gitignore

All 15 notebooks now pass with valid data.

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

pyproject.toml

@@ -35,6 +35,7 @@ dependencies = [
     "geopandas>=1.1",
     "shapely>=2.0",
     "pyproj>=3.6",
+    "statsmodels>=0.14",
 
     # Visualization
     "dash>=3.3",