ground: a task stands where the conversation is about — ladder, record, worktree from that repo, audit restore from it #77

Engine half of the ground design in #76: propose_task{ground}; resolution ladder said → touched → standing in → nothing; TaskNode.Ground/Mode on the record, index and notices; worktree cut from the ground repo (off HEAD, uncommitted changes not carried); reference and mirror modes; audit restore cut from the ground; brief lint (an absolute path in the brief outside the ground re-grounds or refuses); system.md tells the brief author to name the repo, never the method; manual.

Part of #76. Branch ground/engine → PR into feat/task-ground.

Drafted with CodeAF · reviewed and owned by the author