feat: [SEC-7263] Add dependency-scan GitHub Actions workflow

[kparkinson-ld]

feat: SEC-7263 Add dependency-scan GitHub Actions workflow

Summary

Adds a new GitHub Actions workflow that runs dependency scanning on pull requests and pushes to the main branch. This workflow uses LaunchDarkly's centralized common-workflows dependency scanning functionality with Node.js-specific configuration.

The workflow is configured to:

• Trigger on pull requests and pushes to main
• Use the nodejs scan type
• Run on ubuntu-latest
• Inherit repository secrets

Review & Testing Checklist for Human

• Verify scan type: Confirm that types: 'nodejs' is the correct configuration for this repository's tech stack
• Test workflow execution: After merging, create a test PR or push to main to verify the dependency scan workflow runs successfully
• Validate model alignment: Compare against the model PR (launchdarkly/ld-vsts#64) to ensure this follows the same pattern and structure

Notes

• This workflow cannot be fully tested locally since it's a GitHub Actions workflow - verification requires running it on GitHub
• The workflow depends on launchdarkly/common-workflows/.github/workflows/dependency-scan.yml@main being available and functional
• Part of a broader initiative to add dependency scanning across multiple LaunchDarkly repositories

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Requested by: @kparkinson-ld
Link to Devin run: https://app.devin.ai/sessions/04e1232119fc4dda956196fe0edc593f

[devin-ai-integration]

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[kparkinson-ld]

Duplicate.