sync: add cross-subsystem event bus for config consistency

Add EventBus with loop guards to keep firewall, dnsmasq, wireguard,
and network configs consistent. Handlers emit SyncEvent after mutations;
subscribers compute diffs and write JSON without manual cascade loops.

daemon/handlers/nginx.py

@@ -457,7 +457,12 @@ def update_domain(_request: Any, body: dict[str, Any] | None) -> dict[str, Any]:
 
     # Path removal: if body has `path` key (string) but no `paths`/`backend`/`headers`
     path_to_remove = body.get("path")
-    if path_to_remove is not None and "paths" not in body and "backend" not in body and "headers" not in body:
+    if (
+        path_to_remove is not None
+        and "paths" not in body
+        and "backend" not in body
+        and "headers" not in body
+    ):
         paths = entry.get("paths", {})
         if path_to_remove in paths:
             del paths[path_to_remove]