ci: auto-sync CLI docs to docs repo on release

[jason-rl]

Summary

• Adds a sync-docs job to the release workflow that automatically opens a PR in runloopai/docs with updated CLI command reference when release-please creates a new release
• Fixes generate-command-docs.js to create the output file when an explicit --docs-path is provided (previously it silently skipped if the file didn't exist)

The sync-docs job runs in parallel with publish, uses runloopai/create-pull-request (same pattern as runloop-fe's keycloak version sync), and no-ops if there's no diff.

Test plan

• Verify DEPLOY_APP_CLIENT_ID var and DEPLOY_APP_PRIVATE_KEY secret are accessible from this repo and the app has write access to runloopai/docs
• Trigger a release and confirm the sync-docs job runs and creates a PR in runloopai/docs
• Verify no PR is created when the generated MDX has no diff from what's already in docs

🤖 Generated with Claude Code