Butterfly effect

[javanhut]

Butterfly Timelines and Interactive Commit Squashing
This PR introduces two major features that enhance the branching workflow and commit history management in Ivaldi VCS.
Butterfly Timelines
Adds experimental timeline sandboxes with bidirectional synchronization:

• Create isolated experimental branches that track their parent timeline
• Sync changes up to parent (ivaldi timeline butterfly up) when experiments succeed
• Sync parent changes down (ivaldi timeline butterfly down) to keep experiments current
• Nested butterfly support with cascade deletion
• Automatic divergence point tracking for safe merging
  Interactive Shift Command
  Implements modern commit squashing as an alternative to git rebase -i:
• Arrow-key navigation to select commit ranges interactively
• Multiple modes: interactive selection, --last N commits, or specify start/end commits
• Combined commit message suggestions with user override
• Force-push safety warnings and explicit confirmations
• Auto-generated seal names for squashed commits
  Additional Improvements
• Fixed directory exclusion in gather command to properly handle ignore patterns before directory traversal
• Added --force flag to upload command with comprehensive safety checks and warnings
• Enhanced submodule support documentation
• Updated Git comparison table and feature documentation
  Breaking Changes
  None. All new features are additive.
  Documentation
  Complete documentation added for:
• Butterfly timeline workflows and commands
• Shift command usage and examples
• Updated getting started guide with new features
• Enhanced Git migration guide