fix(browser): drain route handlers before closing context

[nichenqin]

Changes

Wait for in-flight Playwright page route handlers before disposing their browser context. Context cleanup still runs if draining fails. This fixes the link-picker runner teardown error observed during teable-ee #3518 without suppressing route failures.

Verification

• Real Chromium smoke: immediate context disposal reproduces route.fetch: Request context disposed; draining routes allows the same request and delayed fulfillment to finish.
• pnpm check:types: passed, 361 files.
• Prettier check on the changed file: passed.

No production deployment or automatic merge.

[nichenqin]

The real browser case link/y554-picker-keeps-selection-across-tabs is running against repaired teable-ee head 43929b7aac using this lab branch: https://github.com/teableio/teable-e2e-lab/actions/runs/35041620365 . The local deterministic Chromium lifecycle smoke and PR pnpm check already passed. No merge performed.

[nichenqin]

Follow-up: the first real-browser run was workflow-green but contained route.fulfill: Route is already handled!; it is not clean acceptance.

Root cause reproduced with the pinned Playwright 1.57 and two concurrent delayed routes: unrouteAll({ behavior: "wait" }) clears the client route list before draining. The first completed handler can then unregister server interception while a second handler still intends to fulfill.

The runner now drains its delayed response promises before unregistering interception and aborts newly arriving requests during shutdown. Rejected in-flight operations still propagate after cleanup.

Deterministic Chromium smoke: old lifecycle reproduced the exact Route is already handled! error; the new lifecycle completed both requests with zero errors. Typecheck passed (361 files). A new real-browser CI run will verify the committed follow-up.

[nichenqin]

Clean acceptance on lab head 659fd80 against teable-ee 43929b7aac: https://github.com/teableio/teable-e2e-lab/actions/runs/35042727730

• Real link-picker browser regression: 1 passed.
• Downloaded and inspected the complete job log: no Unhandled Errors, route.fetch disposal failure, or route.fulfill already-handled failure.
• Run acceptance/comparison job: passed.
• Latest PR pnpm check and CLA checks: passed.
• Local two-concurrent-route reproduction on Playwright 1.57: old lifecycle reproduced the exact already-handled error; new lifecycle had zero errors.

This supersedes the earlier workflow-green run that still contained an unhandled rejection. No merge performed.