fix(frontend): initializeStores dedup + retryAllMessages guard + as any cleanup

- index.ts: add _storesInitialized guard to prevent triple initialization
- offlineStore.ts: add isRetrying mutex for retryAllMessages concurrency
- PropertyPanel.tsx: replace 13x (data as any) with typed d accessor
- chatStore.ts: replace window as any with Record<string, unknown>
- kernel-*.ts: replace prototype as any with Record<string, unknown>
- gateway-heartbeat.ts: delete dead code (9 as any, zero imports)

desktop/src/store/index.ts

@@ -84,11 +84,16 @@ import { setConfigStoreClient } from './configStore';
 import { setSecurityStoreClient } from './securityStore';
 import { setSessionStoreClient } from './sessionStore';
 
+let _storesInitialized = false;
+
 /**
  * Initialize all stores with the shared client.
  * Called once when the application mounts.
+ * Guard ensures it only runs once even if called from multiple connection paths.
  */
 export function initializeStores(): void {
+  if (_storesInitialized) return;
+  _storesInitialized = true;
   const client = getClient();
 
   // Inject client into all stores