fix(health): use real telemetry, fix hardcoded thresholds

- Utilization pillar reads firmware channel_utilization (max of infra
  nodes) instead of estimating from packet counts × 200ms
- is_online uses configured threshold, not hardcoded 24 hours
- Updated defaults: offline 2h (was 24h), battery warning 30% (was 20%)
- Utilization thresholds: 20/25/35/45% matching real Meshtastic behavior
- Behavior pillar threshold aligned with notification config (7200/day)
- has_solar marked as dead code pending Solar Quality Engine

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

meshai/config.py

@@ -282,9 +282,9 @@ class MeshIntelligenceConfig:
     enabled: bool = False
     regions: list[RegionAnchor] = field(default_factory=list)  # Fixed region anchors
     locality_radius_miles: float = 8.0  # Radius for locality clustering within regions
-    offline_threshold_hours: int = 24  # Hours before node considered offline
+    offline_threshold_hours: int = 2  # Hours before node considered offline
     packet_threshold: int = 500  # Non-text packets per 24h to flag
-    battery_warning_percent: int = 20  # Battery level for warnings
+    battery_warning_percent: int = 30  # Battery level for warnings
 
     # Alert settings
     critical_nodes: list[str] = field(default_factory=list)  # Short names of critical nodes (e.g., ["MHR", "HPR"])

meshai/mesh_data_store.py

@@ -745,9 +745,11 @@ class MeshDataStore:
 
         node.last_heard = ts or 0.0
 
-        # Is online (computed from last_heard)
-        now = time.time()
-        node.is_online = (now - node.last_heard) < 86400 if node.last_heard else False
+        # NOTE: is_online is set by MeshHealthEngine.compute() using the
+        # configured offline_threshold_hours. Don't set it here with a
+        # hardcoded value - let the health engine determine online status.
+        # The health engine runs on every refresh cycle and will set is_online
+        # based on: (now - last_heard) < (offline_threshold_hours * 3600)
 
         # Hops, SNR, RSSI (MM)
         node.hops_away = raw.get("hopsAway")