Add admin-only CRUD endpoints for user management under /api/v1/system/users
with full frontend implementation including create, edit, change password,
and delete operations with self-protection guards.
- Extend AuthDomain interface with ListUsers, GetUser, UpdateUser,
UpdateUserPassword, DeleteUser methods
- Add List, Update, Delete methods to UserStore with shared scanUser helper
- Create UserHandler with 5 endpoints protected by admin middleware
- Complete Users.vue admin page with modals and error handling
- Make CreateUser accept role parameter for atomic user creation
- Fix auth middleware to use database role as source of truth instead of
stale JWT claims, preventing privilege persistence after demotion
- Fix pre-existing gofmt issues in yt_dlp.go and config.go