Adds RemoteDefaultBranch() to git.go that detects the repo's actual default branch by checking origin/HEAD, then falling back to checking for origin/master or origin/main. Updates done.go to use this detection instead of hardcoded "main": - Line 168: CommitsAhead now uses detected default branch - Line 173: Error message uses detected branch name - Line 187: Target branch defaults to detected branch Fixes repos using 'master' as default branch (pre-2020 repos). 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com> Co-authored-by: Steve Yegge <steve.yegge@gmail.com>