Enable CodeQL security scanning

[melvinfoo6776]

What changed

• Enabled Dependabot alerts and Dependabot security updates for the repository.
• Added CodeQL analysis for the Python bridge and Swift app.
• Runs CodeQL on pull requests, pushes to main, and weekly.
• Documented the continuous security coverage.

Validation

• Dependabot alerts endpoint returns zero open alerts.
• Workflow YAML parses successfully.
• Python bridge tests passed.
• Swift sources parsed and the Xcode build passed.
• Repository security audit passed: 15 checks, 0 failures.

[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.