feat: add digest restore mode to rebuild projects from digest.txt

[chiragjoshi12]

Summary

This PR adds reverse-ingestion support so users can reconstruct a project from an existing digest.txt.

What’s included

• Added a new restore module to parse digest blocks (FILE: / SYMLINK:) and rebuild files.
• Added CLI restore mode:
  • --restore
  • --restore-dir
  • --overwrite
• Added safety guard to prevent path traversal (e.g. ../ escaping destination).
• Added restore completion stats in CLI output:
  • number of files
  • number of directories
  • number of symlinks
• Added tests for parsing, restore behavior, CLI flow, and traversal protection.
• Updated README with restore usage examples.

Why

gitingest already converts repositories into prompt-ready digests.
This change enables the reverse workflow: digest back to runnable project structure.

Usage examples

# Restore into current directory
gitingest digest.txt --restore

# Restore into a specific folder
gitingest digest.txt --restore --restore-dir ./restored-project

# Overwrite existing files
gitingest digest.txt --restore --restore-dir ./restored-project --overwrite