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.

webui/static/hoover/api.js

@@ -238,7 +238,13 @@ export function apiSubmit(opts) {
                 }
                 const res = await apiFetch(url, { method, body: b });
                 if (res.ok) {
-                    toast(successMsg, 'success');
+                    const synced = res.data?.synced;
+                    let msg = successMsg;
+                    if (synced && synced.length) {
+                        msg += ' (auto-synced: ' + synced.join(', ') + ')';
+                        synced.forEach(s => modelFetch(s));
+                    }
+                    toast(msg, 'success');
                     if (closeModal) closeModal();
                     if (refresh) {
                         const models = Array.isArray(refresh) ? refresh : [refresh];