Commit messages from the real diff

Description

Write, split, and review git commit messages from the actual staged diff - Conventional Commits or the repo's own convention, a subject that says what changed and a body that says why, breaking-change and issue footers, and splitting mixed changes into focused commits. Use whenever the user asks to commit, "write a commit message", "commit this", "what should the message be", squash or reword commits, or when finishing a task that ends in a commit - even if they only say "save my work" or "check this in".