feat: Dynamic MeshMonitor trigger sync — auto-ignore MeshMonitor commands

Add MeshMonitorSync class that reads trigger patterns from a JSON file
and compiles them to regex. The router checks incoming messages against
these patterns and ignores messages that MeshMonitor will handle.

- New meshai/meshmonitor.py: Pattern compilation and file watching
- MeshMonitorConfig dataclass with enabled, triggers_file, inject_into_prompt
- Router integration: ignore matching messages, inject commands into prompt
- Main loop refresh: watch triggers file for changes without restart

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

config.example.yaml

@@ -66,3 +66,9 @@ weather:
   primary: openmeteo             # openmeteo | wttr | llm
   fallback: llm                  # openmeteo | wttr | llm | none
   default_location: ""           # Default location for !weather (optional)
+
+# === MESHMONITOR INTEGRATION ===
+meshmonitor:
+  enabled: false
+  triggers_file: /data/triggers.json
+  inject_into_prompt: true