Implement 5-pillar health scoring with coverage

- Update HealthScore with coverage pillar (20% weight)
- Adjust weights: Infra 30%, Util 25%, Coverage 20%, Behavior 15%, Power 10%
- Add coverage metrics: avg_gateways, single_gw_count, full_count
- Add health score fields to UnifiedNode for direct sync
- compute() now syncs scores back to UnifiedNode objects
- Coverage scoring penalizes single-gateway nodes

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

meshai/mesh_models.py

@@ -127,6 +127,15 @@ class UnifiedNode:
     public_key: str = ""
     is_mqtt_gateway: bool = False
     via_mqtt: bool = False
+
+    # Health scoring (set by MeshHealthEngine)
+    is_infrastructure: bool = False
+    health_score: float = 100.0
+    infra_score: float = 100.0
+    util_score: float = 100.0
+    coverage_score_node: float = 100.0
+    behavior_score: float = 100.0
+    power_score: float = 100.0
 
 
 @dataclass