feat(notifications): add region tagger with coordinate and NWS zone matching

Adds meshai/notifications/region_tagger.py with:
- haversine_distance() for great-circle distance calculation
- tag_by_coordinates() maps lat/lon to nearest region within radius
- tag_by_nws_zone() maps NWS zone codes to matching regions

Also adds nws_zones field to RegionAnchor in config.py to support
zone-based matching. Default is empty list for backward compatibility.

This is scaffolding for Phase 2 - not yet wired into any adapters.

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

meshai/config.py

@@ -230,6 +230,7 @@ class RegionAnchor:
     description: str = ""          # e.g., "Twin Falls, Burley, Jerome along I-84/US-93"
     aliases: list[str] = field(default_factory=list)  # e.g., ["southern Idaho", "magic valley"]
     cities: list[str] = field(default_factory=list)   # e.g., ["Twin Falls", "Burley", "Jerome"]
+    nws_zones: list[str] = field(default_factory=list)  # NWS zone codes (e.g., ["IDZ016", "IDZ030"])
 
 
 @dataclass