Fork: derive default push URL from dune-project metadata
- Add suggest_push_url function to derive push URL from dune-project source field
- Support github, gitlab, tangled, and uri sources
- Convert https URLs to SSH push format (git@...)
- Prompt with suggested URL as default, user can press Enter to accept
- Fix pp_fork_result to not truncate non-SHA strings like "(fresh package)"
- Add Tangled variant to Dune_project.source_info for tangled.sh sources
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>