docs: credit pstack as the inspiration for cs-stack

[CodeSolutionsLLC]

Thanks for the pull request. See CONTRIBUTING.md for how changes land on main.

Summary

The public README now says, near the top, that cs-stack was inspired by Cursor's pstack, and links the public source: https://github.com/cursor/plugins/tree/main/pstack

This is an ideas credit only. The repository already documents first-party rewrites and does not vendor upstream files, so the new section does not claim any code was copied.

Related issue

No related issue.

How to verify

• Open README.md and confirm the Inspiration section sits under the intro, before Status.
• Confirm the link is exactly https://github.com/cursor/plugins/tree/main/pstack
• Confirm no other files changed.

Checklist

• Evidence recorded. Summary and how to verify are filled in (commands, tests, or links). See verify and playbooks/verify.md.
• CI green. Required checks on this pull request are passing, including validate.
• No secrets. The pull request body and diff have no tokens, PATs, private config, or exploit details. Report security issues privately — SECURITY.md.
• CODEOWNERS human merge (no self-merge). Authors wait for an independent human review and merge. Reviewers are listed in .github/CODEOWNERS. See no-self-merge and human-gate.
• Public language safe. No private credentials, internal roster names, or private links.