Implement comprehensive repository URL generation when copying code snippets, transforming output to include direct permalinks to the code in GitHub, GitLab, or Bitbucket.

Features:

• Automatic git repository detection and remote URL parsing
• Support for GitHub, GitLab, and Bitbucket (including Enterprise/self-hosted)
• Always uses commit SHA for stable permalinks
• Lazy provider detection with extensible architecture
• Graceful degradation when not in a git repo
• Configurable via include_remote_url option (default: true)

Implementation:

• New git.lua module for git operations
• Provider architecture with lazy loading
• Integration into existing utils.format_output
• Comprehensive test coverage for all components
• Updated documentation with examples

Supported URL formats:

• GitHub: /blob/{sha}/{path}#L{start}[-L{end}]
• GitLab: /-/blob/{sha}/{path}#L{start}[-{end}]
• Bitbucket: /src/{sha}/{path}#lines-{start}[:{end}]

Handles edge cases:

• Detached HEAD, submodules, multiple remotes
• Windows path conversion, untracked files
• HTTPS, SSH, and git:// protocol URLs

fixes #1