ai-git-cleanup

From the author

Removes finished local git work in one automatic pass, with no question and no name to type: dead worktrees first (`git worktree remove`, then `git worktree prune`), then branches already merged into the local `main`, then the branches a squash-merged pull request left behind (tree identical to `origin/main`, tagged before deletion). Trigger for "tidy up", "tidy up these branches", "tidy branches", "delete old branches", "start fresh", "limpieza de branches", "limpia branches", or by naming ai-git-cleanup. A branch that is not merged into `main` is left alone — unless its tree is byte-identical to `origin/main`, which is what a squash-merged pull request looks like afterward; the pass deletes those with the proof in hand, tags the tip, and never force-deletes anything else. Not for pushing, not for remote branches, not for opening a pull request.