Production-ready rewrite: UI kit integration, admin backups, sorting, profile editing, and security hardening ...

- Frontend: complete rewrite using gnexus-ui-kit components (GnNavigationShell,
  GnTable, GnTimeline, GnModal, GnToastProvider, GnSkeleton, etc.)
- Frontend: browser route sync (/secrets/:id, /audit/:id), pagination,
  real-time search debounce, skeleton loading states, retry with backoff
- Frontend: profile editing modal, token creation with scope selection,
  import/export, settings metrics, admin users table
- Backend: backup/restore endpoints for PostgreSQL and SQLite via pg_dump/psql
- Backend: admin backup CRUD, file download endpoint
- Backend: stats endpoint, PATCH /me profile endpoint, CORS middleware,
  graceful shutdown logging
- Backend: table sorting (sort_by/sort_dir) in list_secrets
- Backend: OAuth return_to validation, rate limiting on sensitive endpoints
- MCP: validation fixes, tool description improvements, protocol cleanup
- Tests: 44 passing including new backup test suite
- Docker: add postgresql-client, backups volume, deployment docs
- Docs: backup/restore instructions in deployment guide

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Add routes for secret detail pages

Add admin diagnostics UI

Add Docker packaging and admin user UI

Add UI history audit and import flows

Add UI secret and token management actions

Implement initial gnexus-creds MVP scaffold