fix(nws): replace centroid filter with polygon intersection

- Add shapely dependency for geometry intersection
- Replace _point_in_region with _geometry_intersects_region
- Uses Shapely shape() and box() for proper GeoJSON handling
- Avoids false negatives on large alert polygons

Also adds antimeridian-crossing bbox rejection to RegionConfig validator.

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

pyproject.toml

@@ -18,6 +18,7 @@ dependencies = [
     "nats-py>=2.14.0",
     "pydantic>=2,<3",
     "pydantic-settings>=2.7.0",
+    "shapely>=2.0",
     "tenacity>=9.1.4",
 ]