feat(ui): Sentinel view — Yerin global security chat

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/app.js

@@ -22,6 +22,7 @@ const VIEWS = {
   search:          () => import('./views/search.js'),
   inbox:           () => import('./views/inbox.js'),
   'sacred-valley': () => import('./views/sacred_valley.js'),
+  sentinel:        () => import('./views/sentinel.js'),
   jobs:            () => import('./views/jobs.js')
 };