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>

setup/register.ts

@@ -49,7 +49,7 @@ function parseArgs(args: string[]): RegisterArgs {
     trigger: '',
     folder: '',
     channel: 'discord',
-    requiresTrigger: true,
+    requiresTrigger: false,
     assistantName: 'Andy',
     sessionMode: 'shared',
   };