### What problem does this PR solve?
Playwright tests previously depended on cross-file execution order
(`auth -> provider -> dataset -> chat`).
This change makes setup explicit and idempotent via fixtures so tests
can run independently.
- Added/standardized prerequisite fixtures in
`test/playwright/conftest.py`:
- `ensure_auth_context`, `ensure_model_provider_configured`,
`ensure_dataset_ready`, `ensure_chat_ready`
- Made provisioning reusable/idempotent with `RUN_ID`-based resource
naming.
- Synced auth envs (`E2E_ADMIN_EMAIL`, `E2E_ADMIN_PASSWORD`) into seeded
creds.
- Fixed provider cache freshness (`auth_header`/`page` refresh on cache
hit).
Also included minimal stability fixes:
- dataset create stale-element click handling,
- search wait logic for results/empty-state,
- agent create-menu handling,
- agent run-step retry when run UI doesn’t open first click.
### Type of change
- [x] Test fix
- [x] Refactoring
---------
Co-authored-by: Liu An <asiro@qq.com>
### What problem does this PR solve?
This PR adds end-to-end Arabic support in production. It also adds a
full Arabic README
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
- [x] Documentation Update
