bug(git): branch names containing slashes misclassified as file paths

[rocketman-code]

Current Behavior

Running chainsaw diff feature/auth --entry src/index.ts fails with a "file not found" error because the slash in feature/auth triggers the path-like heuristic in classify_diff_arg. The function checks for / before attempting git ref resolution, so valid branch names like feature/auth, bugfix/login, or release/v2 are never tried as git refs.

Expected Behavior

Branch names with slashes should be correctly identified as git refs. The function should attempt git ref resolution before the path-like heuristic, or the heuristic should be scoped more narrowly.

Context

Slash-separated branch names are a common convention (feature/x, bugfix/y, release/z). This makes chainsaw diff unusable with these branch naming patterns.

Technical Details

Relevant Code

src/git.rs:30-37 — classify_diff_arg

let looks_like_path = arg.contains('/')
    || arg.contains(std::path::MAIN_SEPARATOR)
    || path.extension().is_some_and(|ext| ext.eq_ignore_ascii_case("json"));
if looks_like_path {
    return Err(crate::error::Error::DiffFileNotFound(arg.to_string()));
}

The / check fires before the git rev-parse fallback at line 40.