fix: resolve relative paths correctly when creating worktrees from HEAD

[wasabeef]

Summary

This PR introduces several enhancements to git-workers v0.3.0:

1. Custom Path Support for Worktree Creation

• Added a third option "Custom path (specify relative to project root)" when creating the first worktree
• Allows users to specify arbitrary relative paths for flexible worktree organization
• Comprehensive path validation with security checks to prevent path traversal attacks

2. Security and Robustness Improvements

• Worktree Name Validation: Prevents invalid characters, reserved names, and non-ASCII warnings
• File Copy Size Limits: Automatically skips files larger than 100MB with clear warnings
• Concurrent Access Control: File-based locking prevents race conditions during worktree creation
• Path Security: Validates custom paths against traversal attacks and excessive navigation

3. Bug Fixes

• Fixed path resolution for non-bare repositories when creating worktrees from HEAD
• Fixed format string issues to comply with clippy::uninlined_format_args
• Fixed Ubuntu CI compatibility for worktree lock tests (handles different default branch names)

Key Changes

Custom Path Feature

// New validation function for custom paths
fn validate_custom_path(path: &str) -> Result<()> {
    // Comprehensive validation including:
    // - No absolute paths
    // - No excessive parent directory navigation
    // - No git reserved names in path components
    // - Cross-platform compatibility checks
}

Security Enhancements

• Worktree names now reject filesystem-incompatible characters
• File copy operations skip large files (>100MB) and symlinks
• Lock files prevent concurrent worktree creation with automatic stale lock cleanup

Testing

• Added 9 tests for custom path validation
• Added 7 tests for worktree name validation
• Added 6 tests for file size limits
• Added 5 tests for concurrent access control
• All tests pass on both macOS and Ubuntu

Breaking Changes

None - all changes are backward compatible.

Migration Guide

No migration needed. The custom path option is additive and doesn't affect existing workflows.

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