feat(hub): add /database admin surface with Feishu login

Adds a self-contained `/database/*` HTTP surface under hub/src/database:
- /database/admin: Feishu-only login page (Tailwind, light theme)
- /database/dashboard: session-gated sidebar + content shell
- /database/dev-login: DEV ONLY session bypass, double-gated by
  NODE_ENV != production AND HUB_DEV_LOGIN_BYPASS; never active in prod

hub.ts mounts the plugin after the admin plugin so the cookie parser and
/auth/feishu/* routes are available. The dev bypass logic is fully contained
in the database module; admin auth routes are untouched.

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

hub/.gitignore

@@ -5,6 +5,9 @@ dist/
 .env.*
 !.env.example
 .secrets/
+.dev-keyring.json
+.dev-workspaces/
+.dev-skills/
 admin-web/node_modules/
 admin-web/build/
 admin-web/.svelte-kit/