Fix selector injection and close() race condition in browser package

[Copilot]

• Fix selector injection vulnerability in A11yParser.ts
• Fix race condition in PlaywrightContext.ts close() method
• Investigate CI build failures - 12 Playwright integration tests failing in base browser branch and all subsequent runs
• Fix CI: add bunx playwright install chromium --with-deps step to test.yml so Playwright browser binaries are available during bun test

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[sroussey]

@copilot fix build/test issues

[Copilot]

@copilot fix build/test issues

Fixed in commit 15a0c75. The 12 Playwright integration tests were failing because the CI workflow installed the playwright npm package via bun i but never downloaded the actual Chromium browser binary. Added bunx playwright install chromium --with-deps to .github/workflows/test.yml after the bun i step. The remaining 1 failure (TextEmbeddingTask > HuggingFace Transformers > gte-small) is a flaky network/download test that was already inconsistent in the browser base branch (failed in one run, passed in another).