Bind approvals and feedback to the revision they were about

Fixes counterexamples 1-4 from specs/orchestrator.qnt: a repeated
'approve', 'approve rev-1' meant for the architecture, approving on both
channels, and 'approve' plus an afterthought all landed on the next
plan, one the operator had not seen.

- Revisions are numbered across the work item (A4 already required
  monotonic tags; the code numbered per gate), so rev-N names one plan.
- Each reply is stamped on arrival with the revision that was up: in
  Matrix the one whose approval request had been sent (a plain value
  the transport thread reads, restored on boot), in Gitea the latest
  plan comment older than the reply (board.posts).
- Gate.evaluate applies a reply that names no revision only if its stamp
  is the current revision. Otherwise an approval is not applied and
  feedback rejects nothing (it is still in the transcript), and the
  agent says which revision is up. 'approve rev-N' binds by its number.
- Spec A4 states both rules. The model applies them; scenarios 1-4 now
  expect the properties to hold, and both held over 200,000 random
  traces and Apalache's exhaustive check to depth 8.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPQ14L3LikyefCMFBqEbKE

nisse-dev/tests/test_control.py

@@ -128,7 +128,9 @@ def test_start_milestone_requires_approval_first(h: Harness) -> None:
     h.transport.receive("don", "approve")
     h.transport.receive("don", "start milestone 1")
     assert h.state == AWAIT_MILESTONE_SIGNOFF  # it was rejection feedback
-    h.transport.receive("don", "approve rev-2")
+    # Revisions run across the task: arch rev-1, milestone-1 rev-2, and
+    # after that rejection milestone-1 rev-3.
+    h.transport.receive("don", "approve rev-3")
     h.transport.receive("don", "start milestone 1")
     assert executed(h)