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/lib/kernel-a2a.ts

@@ -8,7 +8,7 @@ import { invoke } from '@tauri-apps/api/core';
 import type { KernelClient } from './kernel-client';
 
 export function installA2aMethods(ClientClass: { prototype: KernelClient }): void {
-  const proto = ClientClass.prototype as any;
+  const proto = ClientClass.prototype as unknown as Record<string, unknown>;
 
   // ─── A2A (Agent-to-Agent) API ───