feat: Add Windows Playwright testing to nightly builds (#12221)

* feat: add Windows support for Playwright tests in nightly builds

- Add windows-latest as runner option in typescript_test.yml
- Update Playwright browser installation to be OS-aware (Windows doesn't support --with-deps)
- Add matrix strategy to nightly_build.yml to run tests on both Linux and Windows
- Update Slack notifications to indicate multi-platform testing
- Tests now run in parallel on ubuntu-latest and windows-latest

This enables catching Windows-specific regressions early in the nightly build process.

* fix: add shell: bash to all script steps for Windows compatibility

Windows runners default to PowerShell which doesn't understand bash syntax.
All steps with bash scripts now explicitly specify shell: bash to ensure
cross-platform compatibility.

* feat: make Windows Playwright tests non-blocking initially

Add continue-on-error for Windows tests to allow nightly builds to succeed
even if Windows-specific issues are found. This gives us visibility into
Windows bugs without blocking releases.

Windows tests will still run every night and report failures, but won't
block the build. Once Windows tests are stable, we can remove this flag.

* chore: fix white space

chore: fix white space

* fix: replace matrix strategy with separate jobs for Windows Playwright tests

- GitHub Actions reusable workflows don't support matrix strategy
- Split frontend-tests into frontend-tests-linux and frontend-tests-windows
- Windows tests are non-blocking (continue-on-error: true)
- Updated all job dependencies and Slack notification logic
- Addresses PR review comment about matrix limitation

* chore: trigger workflow validation refresh

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Co-authored-by: Adam Aghili <Adam.Aghili@ibm.com>