Find workspace files by path pattern.

Usage:
- `pattern` is a glob matched relative to the workspace execution root.
- Use `../...` segments in the pattern when you need to search outside the workspace execution root.
- Use `tmp/...` to search inside the managed workspace tmp directory.
- Use this tool to discover candidate files when you know naming or directory conventions.
- Results are returned as relative workspace paths.
- If you need to search file contents instead of file names, use `grep`.
- If you already know the exact path, use `read` directly instead of globbing first.
