Git review cannot stage files with non-ASCII names because diff paths stay escaped

[cristicretu]

The diff parser preserves Git's C-style filename escapes instead of decoding them. The per-file Git actions then receive a path that does not exist.

Reproduction

1. Initialize a repository with a committed baseline and standard core.quotePath=true.
2. Create an untracked file named café.txt.
3. Open Working changes and click the file's Stage action.

Reproduced result

An isolated Rust harness imported the unchanged diff.rs and git_review.rs from main and called load_local_diff(root, DiffLayer::Working), then passed the resulting file path to GitRepository::stage_paths.

parsed path: "caf\\303\\251.txt"
stage result: fatal: pathspec 'caf\303\251.txt' did not match any files
expected path: "café.txt"

The path-equality regression assertion failed. All Git mutations were confined to disposable fixture repositories.

Cause and impact

• diff_path strips the surrounding quotes but does not decode octal or backslash escapes.
• parse_unified_diff_bytes makes that string the authoritative DiffFile.path.
• The inspector sends that path directly to per-file Stage and Unstage.
• git_command does not change Git's path-quoting configuration.

This also gives file opening and quoted diff evidence the wrong filename. Whole-hunk patch bytes are retained separately; this report specifically concerns decoded file identity and file-scoped actions.

Expected behavior

Parse Git-quoted path bytes faithfully and preserve the actual repository-relative filename. Simply disabling core.quotePath does not solve quotes, tabs, or backslashes in filenames.

Add integration cases for a non-ASCII filename, quoted/backslash characters, and whitespace; assert both the parsed path and successful per-file staging.

Validated against main 1196d89 with an isolated Cargo harness using production modules. No product files were modified.