feat(mesh): config-driven regions with stale purge and coverage fix

- Extended RegionAnchor with local_name, description, aliases, cities
- Moved region geographic context from hardcoded Python to config.yaml
- Added 7-day stale node purge in _do_refresh (556 → 267 nodes)
- Fixed coverage lookup: str(node_num) → node_num (int key)
- Added bidirectional neighbor lookup for better region assignment
- Dynamic geography building in router from config
- Reporter reads region context from config instead of hardcoded dict

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

meshai/config.py

@@ -179,11 +179,15 @@ class MeshSourceConfig:
 
 @dataclass
 class RegionAnchor:
-    """A fixed region anchor point."""
+    """A fixed region anchor point with geographic context."""
 
     name: str = ""
     lat: float = 0.0
     lon: float = 0.0
+    local_name: str = ""           # e.g., "Magic Valley"
+    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"]
 
 
 @dataclass