Add repository security tooling

[WebCrew]

This pull request strengthens Parlyn's GitHub safety net without changing engine runtime behavior.

Included

• switch CI dependency installation from npm install to reproducible npm ci
• enable npm caching in GitHub Actions
• add weekly Dependabot checks for npm dependencies
• add CodeQL analysis for JavaScript/TypeScript on pushes, pull requests and a weekly schedule

Why

Parlyn is now public and growing. These checks provide automated feedback for dependency risks, code-security issues, syntax/build regressions and reproducibility before changes reach main.

No engine features or project data formats are changed by this PR.

[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.