Allow exclude_paths to suppress rewrites in vendor or forked code

[CasperKristiansson]

Summary

Add an exclude_paths option so users can prevent rewrites under specific directories (e.g., vendored dependencies, submodules, or forks) while keeping broad discovery enabled elsewhere.

Why

Large repos often track third-party code they do not want the action to modify. Today the only workaround is to override the entire paths glob list, which is brittle.

What needs to happen

• Introduce an exclude_paths input that accepts newline-separated globs.
• Apply the exclusions after resolving default or user-specified paths.
• Reflect exclusions in logs and the change matrix so users know why files were skipped.
• Add tests ensuring exclusions take precedence and do not affect unrelated files.
• Document the new knob in README and examples.

References

• Roadmap capabilities item: "Exclusions".

Acceptance criteria

• Users can configure exclusions without redefining the full include list.
• Change matrix and summary note when files were ignored due to exclusions.
• Documentation includes a usage example.