ci: add CodeQL for JavaScript/TypeScript, Actions and C# (#287)

[rowkav09]

Part of #287. Replaces the parked #128 now that code scanning is free on the public repo.

• Advanced-setup workflow covering the three languages GitHub detects: javascript-typescript, actions and csharp (the Windows launcher, scripts/windows-launcher.cs). All use build-mode: none, so there's no build step. security-extended queries.
• Runs on every PR, on pushes to main, and weekly (Mon 04:17 UTC) to catch new queries against unchanged code.
• Actions pinned by SHA (checkout v4, codeql-action v4.38.1), persist-credentials: false. The job gets security-events: write only, and the workflow default is contents: read.
• Code scanning default setup is currently not-configured, so this workflow won't conflict with it. Don't turn default setup on as well: GitHub rejects advanced-setup uploads while default setup is enabled.

[rowkav09]

/mira pause

[github-advanced-security]

You are seeing this message because GitHub Code Scanning has recently been set up for this repository, or this pull request contains the workflow file for the Code Scanning tool.

What Enabling Code Scanning Means:

• The 'Security' tab will display more code scanning analysis results (e.g., for the default branch).
• Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results.
• You will be able to see the analysis results for the pull request's branch on this overview once the scans have completed and the checks have passed.

For more information about GitHub Code Scanning, check out the documentation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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