fix(git): keep status paths relative to cwd

[fengjikui]

Fixes #2373.

Summary

• keep compact rtk git status paths relative to the caller's current subdirectory
• preserve paths outside the subdirectory as ../..., matching native git status --short
• keep quoted paths, renames, current-directory untracked dirs, and non-ASCII prefixes covered by tests

Root cause

Compact status uses git status --porcelain -b, whose v1 porcelain paths are repo-root relative. In a monorepo subdirectory, that made RTK print paths like apps/web/local_subdir/file.py while native git status prints local_subdir/file.py.

Validation

• cargo fmt --all
• cargo test test_build_status_command
• cargo test test_format_status_output_relative
• cargo test test_git_status_paths_are_relative_to_current_subdir -- --ignored
• manual temp-repo checks for sibling paths and non-ASCII subdirectory prefixes
• cargo clippy --all-targets
• cargo test --all