Removes DEFAULT_MODEL in favour of a force_model setting configurable
via the admin UI. When set, every proxy request's model field is
overridden, preventing uncoordinated model switches during lab sessions.
Updates schemas, admin API, all three proxy endpoints, frontend,
init_db, and docs (README, DOCKERHUB, KURZANLEITUNG).
- Remove User/Quota models; quota fields now live directly on APIKey
- Admin UI: login, API key management, settings (Ollama URL/model), proxy info display
- .env/.env.example: ADMIN_PASSWORD, PROXY_HOST/PORT, DATABASE_URL, APP_TZ
- Admin API runs on 127.0.0.1 only; proxy host/port configurable
- API keys support optional expires_at; verified against Europe/Berlin timezone
- Daily/monthly quota resets use Europe/Berlin midnight boundary
- Fix all tests to use new flat model; add expiry tests
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
