fix: address review feedback for per-group queue reliability

- Fix startup recovery running before WhatsApp connects, which could
  permanently lose agent responses by advancing lastAgentTimestamp
  before sock is initialized
- Add 5s retry on container failure so messages aren't silently dropped
  until a new message arrives for the group
- Use `container stop` in shutdown instead of raw SIGTERM to CLI wrapper,
  ensuring proper container cleanup
- Replace unnecessary dynamic imports with static imports in processTaskIpc
- Guard JSON.parse of DB-stored last_agent_timestamp against corruption
- Validate MAX_CONCURRENT_CONTAINERS (default 5, min 1, NaN-safe)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/config.ts

@@ -31,9 +31,9 @@ export const CONTAINER_MAX_OUTPUT_SIZE = parseInt(
   10,
 ); // 10MB default
 export const IPC_POLL_INTERVAL = 1000;
-export const MAX_CONCURRENT_CONTAINERS = parseInt(
-  process.env.MAX_CONCURRENT_CONTAINERS || '3',
-  10,
+export const MAX_CONCURRENT_CONTAINERS = Math.max(
+  1,
+  parseInt(process.env.MAX_CONCURRENT_CONTAINERS || '5', 10) || 5,
 );
 
 function escapeRegex(str: string): string {