The create, edit, and reset-password modals were using 'modal-overlay'
and 'modal' classes instead of the standard 'modal active' and
'modal-content' pattern, making them invisible due to CSS rules that
hide .modal elements without the .active class.
Add complete multi-user support with role-based access control:
Backend:
- Add users CRUD endpoints (GET/POST/PUT/DELETE /api/users) with admin-only guards
- Add display_name column to users table with ALTER TABLE migration
- Fix auth to use session-based user identity (not hardcoded 'admin')
- Add POST /api/auth/logout to revoke server-side sessions
- Add require_admin() and extract_session() helpers for clean RBAC
- Guard all mutating endpoints (clients, providers, models, settings, backup)
Frontend:
- Add Users management page with create/edit/reset-password/delete modals
- Add role gating: hide edit/delete buttons for viewers on clients, providers, models
- Settings page hides auth tokens and admin actions for viewers
- Logout now revokes server session before clearing localStorage
- Sidebar shows real display_name and formatted role (Administrator/Viewer)
- Fix sidebar header: single logo with onerror fallback, renamed to 'LLM Proxy'
- Add badge and btn-action CSS classes for role pills and action buttons
- Bump cache-bust to v=7
