feat: add force push support to push command

[yxrxy]

Fixes #68

功能：添加--force参数，当本地分支历史领先但存在提交改写时，强制将本地分支推送到远程并覆盖对应分支

[Copilot]

Pull request overview

This PR adds force push support to the push command, implementing the ability to override remote history when local and remote branches have diverged. The implementation adds a --force flag and includes an ancestor checking mechanism to determine if a push requires force mode.

Key changes:

• Adds --force/-f CLI flag to enable force push operations
• Implements is_ancestor function using BFS to check for fast-forward compatibility
• Improves error handling for missing branches
• Updates remote tracking branches after successful push
• Adds test coverage for force flag parsing

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 7 comments.

[yxrxy]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 7 comments.

当前暂无法实现 push 的集成测试，缺少真实的 HTTP 请求环境，目前pull，push的测试目录都是空的