Optimize CI/CD pipeline with workspace-detector for changed packages

[dodok8]

Summary

Add workspace-detector workflow to optimize CI/CD pipeline by detecting changed packages and running tests, lints, and publish operations only on affected packages.

Affected Area

• GitHub Actions workflow configuration
• CI/CD pipeline (test, lint, publish jobs)
• @fedify/cli package testing

Reason / Context

Currently, the CI/CD pipeline runs tests, lints, and publish operations on all packages regardless of which files were actually changed. This wastes CI resources and increases build times unnecessarily. By implementing a workspace-detector workflow, we can:

• Identify which packages have been modified in a given PR or commit
• Run tests and lints only on changed packages
• Optimize CI execution time and resource usage
• Add conditional logic to run deno task test-init specifically when @fedify/cli is changed.

This approach is especially valuable in a monorepo with multiple packages where changes are often isolated to specific packages.

Checklist

1. Implement workspace-detector workflow to detect changed packages
2. Integrate workspace-detector output into existing test workflows
3. Update lint workflow to only run on changed packages
4. Update the publish workflow to only publish changed packages
5. Add a conditional step to run the deno task test-init when @fedify/cli is modified
6. Test the workflow with sample PRs affecting different packages
7. Update documentation if needed