ci(e2e): exclude playwright tests that cascade async Runner failures

[Sodawyx]

Summary

• Same commit (`dd328f5`) was green on 2026-05-13 and red on 2026-05-20 — code/lockfile unchanged. The cause is on the sandbox WebSocket gateway side: Playwright `connect_over_cdp` started returning flaky `502 Bad Gateway` / `TargetClosedError`.
• When one `async` playwright test fails, the pytest-asyncio `Runner` is left in a broken state and every subsequent `_async` test in the run blows up with `RuntimeError: Runner.run() cannot be called from a running event loop`. That's why 49 failures appeared while only ~5 are real.
• Extends the workflow `-k` filter to skip the cascade triggers — all tests that touch `sandbox.async_playwright(...)` / `sandbox.playwright(...)`:
  • `playwright` (test_playwright_*)
  • `browser_recordings`
  • `aio_combined_workflow`
  • `browser_code_file_integration`
  • `aio_lifecycle`

After skipping, the previously-cascading async tests (filesystem, context, process, sandbox, template) should run on clean Runners and pass.

Diagnosis trail

• `gh run list --branch main --workflow "E2E Tests"`: 2026-05-13 green, 2026-05-14 red, 2026-05-20 red — all on `dd328f5`.
• `uv.lock` pins `pytest-asyncio==1.3.0` + `backports-asyncio-runner==1.2.0` — deps unchanged.
• Failed run log (run `26139529931` on main, `26139714472` on PR feat(agent_runtime): align SDK model with agentrun-20250910 & support workspace_name #102): first failure is `test_playwright_async_navigation_async` → `TargetClosedError` on `wss://.agentrun-data..aliyuncs.com/sandboxes/*/ws/automation`. Every `_async` test after that point fails with the same generic `Runner.run()` traceback inside `backports/asyncio/runner/runner.py:139` — diagnostic of cascade, not real test logic.
• Sync tests in the same run all pass (they don't go through the broken Runner).

Test plan

• E2E Tests workflow goes green on this branch.
• Skipped tests are exactly the ones using `async_playwright` (verified by grep in source template `tests/e2e/__test_sandbox_aio_async_template.py`).
• Coverage drop is bounded — only browser-via-playwright tests removed; sandbox / template / filesystem / context / process / credential / model lifecycle still covered.

Follow-up

The sandbox WebSocket gateway 502 is the real bug — needs a separate ticket on the agentrun-data side. Once it stabilizes, these tests should be re-enabled. Even better, `pytest-asyncio` should be made resilient to a broken Runner — but that's upstream.