Jujutsu mutation and stable-ID discipline

When a repository contains .jj/, perform every repository mutation through Jujutsu; use Git only for read-only inspection or capabilities unavailable in Jujutsu. Avoid interactive flags, provide explicit -m messages for describe or commit operations, prefer stable change IDs over commit hashes, and never rebase or describe immutable commits. Treat conflicts as recorded commit state: after jj rebase, jj new, or jj squash, run jj st, resolve markers manually, and verify with both jj st and jj log. Use jj undo or operation-log recovery when needed.