feat(v2): track unregistered senders + setup improvements

- Add unregistered_senders table to capture dropped message origins
  (one row per sender, upserted with message_count and last_seen)
- Add inbound DM logging to chat-sdk-bridge for debugging
- Add vercel CLI to base container image
- Install vercel-cli and frontend-engineer container skills
- Default requiresTrigger to false in register step

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/channels/chat-sdk-bridge.ts

@@ -178,6 +178,7 @@ export function createChatSdkBridge(config: ChatSdkBridgeConfig): ChannelAdapter
       // DMs — always forward + subscribe
       chat.onDirectMessage(async (thread, message) => {
         const channelId = adapter.channelIdFromThreadId(thread.id);
+        log.info('Inbound DM received', { adapter: adapter.name, channelId, sender: (message.author as any)?.fullName ?? (message.author as any)?.userId ?? 'unknown', threadId: thread.id });
         await setupConfig.onInbound(channelId, null, await messageToInbound(message));
         await thread.subscribe();
       });