Pr To Main Cleanup

Since squash merges don't leave the commit history that lets git auto-detect merged branches, this uses force delete and chains the whole sequence together: switch to main, pull latest, nuke the local branch with -D, then delete the remote. It's triggered by saying "cleanup", "ブランチ削除", or similar phrases in English or Japanese. Saves you from manually typing that four-command chain every time, which is the kind of small friction that adds up when you're merging frequently.