Sweep the silently auto-merged leftovers of the superseded #587 wire layer:
the PlanModeState interface and planMode/setPlanMode entries in the sessions
API and rpc map, the fixture plan RPC spec, the composer.controls README
paragraph and spec assertions, the old-format plan-mode snapshot, and the
two Agent Notes written against the RPC design (to be rewritten for the
projection reattachment). ChatView/PendingCard keep the approval-only
pending rendering; QuestionComposer improvements ride along unchanged.