feat(vcs): Address PR review comments for base_ref detection

- Fix UTF-8 error handling with proper anyhow::Error conversion
- Add explicit type annotations for closure error handling
- Use anyhow::Error consistently instead of git2::Error for better error messages
- Implement cleaner error propagation as suggested in review

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: runningcode

src/utils/vcs.rs

@@ -257,21 +257,23 @@ pub fn git_repo_base_ref(repo: &git2::Repository, remote_name: &str) -> Result<O
     let remote_branch_name = format!("refs/remotes/{remote_name}/HEAD");
     let remote_ref = repo
         .find_reference(&remote_branch_name)
-        .or_else(|_| {
+        .or_else(|_| -> Result<git2::Reference, anyhow::Error> {
             // If remote/HEAD doesn't exist, try to query the remote for its actual default branch
             let mut remote = repo.find_remote(remote_name)?;
             remote.connect(git2::Direction::Fetch)?;
             let default_branch_buf = remote.default_branch()?;
-            let default_branch = default_branch_buf.as_str().unwrap();
+            let default_branch = default_branch_buf
+                .as_str()
+                .ok_or_else(|| anyhow::anyhow!("Default branch contains invalid UTF-8"))?;
 
             // Convert "refs/heads/main" to "refs/remotes/origin/main"
             let branch_name = default_branch
                 .strip_prefix("refs/heads/")
                 .unwrap_or(default_branch);
             let remote_branch = format!("refs/remotes/{remote_name}/{branch_name}");
-            repo.find_reference(&remote_branch)
+            Ok(repo.find_reference(&remote_branch)?)
         })
-        .map_err(|e| {
+        .map_err(|e: anyhow::Error| {
             anyhow::anyhow!(
                 "Could not find remote tracking branch for {}: {}",
                 remote_name,