feat(tests): add comprehensive Playwright integration tests for all API endpoints
- tests/01: add graceful login timeout handling with try/catch
- tests/02: migrate from isolated request.newContext to uiLogin + page.request pattern
- tests/03: workspace members, platform users CRUD, billing, alert-config
- tests/04: room messages, room list, repo list/detail APIs
- tests/05: project members CRUD, project detail, project billing
- tests/06: API token CRUD, logout, health check
- tests/07: AI provider/model/version/pricing CRUD
- tests/08: admin user CRUD, role CRUD
All tests use consistent checkBackendAvailable() + uiLogin() pattern with
graceful degradation (test.skip) when backend is unreachable.
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