feat: Add Windows Playwright test fixes to RC (#12265)

* feat: Add Windows Playwright tests to nightly builds

- Add windows-latest to typescript_test.yml runner options
- Add shell: bash to all script steps for cross-platform compatibility
- Split Playwright installation into OS-aware steps (Linux uses --with-deps, Windows/macOS/self-hosted don't)
- Fix artifact naming with OS prefix to prevent conflicts: blob-report-${{ runner.os }}-${{ matrix.shardIndex }}
- Split frontend-tests into separate Linux and Windows jobs in nightly_build.yml
- Add ref parameter to all test jobs to checkout code from release branch
- Add resolve-release-branch to needs dependencies
- Update Slack notifications to handle both Linux and Windows test results
- Windows tests are non-blocking (not checked in release-nightly-build condition)
- Update .secrets.baseline with new line number (263 -> 347) for LANGFLOW_ENG_SLACK_WEBHOOK_URL

Fixes LE-566

* fix: Use contains() for self-hosted runner detection

- Replace exact string equality (==, !=) with contains() for substring matching
- Fixes issue when inputs.runs-on is array format: '["self-hosted", "linux", "ARM64", ...]'
- Ensures self-hosted Linux runners correctly skip --with-deps flag

Addresses CodeRabbit feedback on PR #12264