Add Codex plugin manifest and scanner CI

[internet-dot]

I opened this to add a scanner-only check for the Codex plugin surface in the repo.

A couple of repo-specific details I checked first:

• Manage test cases, execute manual or automated tests, debug issues, and even fix code—directly within tools like Cursor, Claude, or any MCP-enabled client, using plain English
• Easily connect the BrowserStack Test Platform to your favourite AI tools, such as IDEs, LLMs, or agentic workflows
• Auto-analyze, diagnose, and even fix broken test scripts right in your IDE or LLM. Instantly fetch logs, identify root causes, and apply context-aware fixes. No more debugging loops

The current local scan came back 85/100 (grade B).

This PR only adds the scanner workflow. It does not touch runtime code or release behavior.
If you would rather wire it in a different workflow file, I can adjust the branch.