- Batch all refs into one git fetch command instead of separate commands per ref
- Apply --force globally when any ref needs it or remote.Force is set
- Reduces git subprocess calls from N to 1, improving performance
- Maintains same functionality while eliminating inefficient loop

The List method was blindly setting HEAD to point to the configured default
branch without verifying the branch actually exists. This caused "couldn't
find remote ref" errors when cloning repositories with misconfigured default
branches (e.g., pointing to non-existent "master" branch).

Changes:
- Add validation to check if configured default branch exists
- Implement fallback logic: prefer "main" branch, then first available branch
- Add warning logs when falling back to different branch
- Handle edge case of repositories with no branches
- Prevent fatal clone errors due to invalid HEAD references

Fixes scenarios where repository default branch configuration points to
non-existent branches, improving clone reliability and user experience.