fix(tool): preserve special paths in file_find

[RerankerGuo]

Description

file_find parsed git ls-files and git ls-tree as newline-delimited
text. Git C-quotes paths containing non-ASCII or special characters in that
mode, so the tool returned strings such as:

"unicode-\346\265\213\350\257\225.go"

Those strings are display representations rather than real repository paths,
so a follow-up file_read cannot open the selected file.

This change requests NUL-delimited output from both Git commands and parses the
raw paths by NUL. Workspace and commit-mode discovery now preserve Unicode,
tabs, quotes, and other Git-valid path bytes without changing the existing
newline-delimited file_find response contract.

Paths containing literal newlines are covered at the enumeration layer only;
representing those unambiguously in the final text response is outside this
PR's scope.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactoring (no functional changes)
• Documentation update
• CI / Build / Tooling

How Has This Been Tested?

• make check
• make test
• make build
• make coverage - 90.2%, meeting the 90% threshold
• Real temporary Git repositories in workspace and commit modes

Before the fix, the new regression test failed because listGitFiles returned
Git's C-quoted display strings instead of the original paths. After the fix,
the same test passes for Unicode, tab, quote, and newline path cases in both
enumeration modes. The full internal/tool package also passes with the race
detector.

Self-review used OCR Delegation Mode with the host agent:
2/2 changed files reviewed, 0 skipped, 0 findings.

Checklist

• My code follows the project's coding style (go fmt, go vet)
• I have performed a self-review of my code
• I have added tests that prove my fix is effective or my feature works
• New and existing unit tests pass locally with my changes
• Documentation is not required for this internal path enumeration fix
• I have signed the CLA

Related Issues

No existing issue found. All open issues, pull request text, and open pull
request changed files were checked before implementation; no competing
file_find path-enumeration change was found.

[github-actions]

✅ OpenCodeReview: Review complete: 0 finding(s) across 1 selected item(s).