feat: Auth UX & Admin Console Polish for v0.6.5-beta

[DeepZone]

Motivation

• Improve authentication UX by surfacing the current user and role in the UI and providing a robust logout flow.
• Provide an admin-facing user management console so administrators can create, update and deactivate users without exposing password hashes.
• Make navigation role-aware (admin/operator/viewer) and prevent accidental access to forbidden views in the client.
• Bump release to v0.6.5-beta and document the new auth/roles behavior in README and release notes.

Description

• Frontend: add structured user types and API calls in frontend/src/types.ts and frontend/src/api.ts (User, UserCreatePayload, UserUpdatePayload, listUsers, createUser, updateUser, getMe, logout).
• Frontend: persist currentUser in frontend/src/App.tsx, improve logout (onLogout) to clear local state on failure, add dashboard auth-capability card, and implement view guards for forbidden sections.
• Frontend: update frontend/src/components/Layout.tsx to show Angemeldet als <username> · <role>, add role-aware navigation and visible Logout button, and add Users nav entry for admins.
• Frontend: add admin-only frontend/src/components/UsersView.tsx for listing, creating, updating (role / is_active / password reset) users with solid UX for loading, errors and success.
• Backend: harden backend/app/api/routes_users.py to validate roles, never return password_hash, and include created_at/updated_at/last_login_at in responses.
• Backend/System: bump reported version strings to v0.6.5-beta in backend/app/core/system_status.py, backend/app/api/routes_system.py, and backend/app/main.py and update backend/pyproject.toml.
• Docs: update README.md, RELEASE_NOTES.md, docs/operations/security.md, and docs/operations/troubleshooting.md to describe roles, admin user management, logout behavior and known limitations.

Testing

• Ran backend test suite with cd backend && pytest -q, resulting in all tests passing (86 passed).
• Built the frontend with cd frontend && npm run build, which completed successfully producing a production build.

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Codex Task