fix(server,app): close archive and undo races found in review

- An archive request now claims the workspace's archive queue before
  looking up the workspace, so an undo sent right behind it cancels it
  instead of running first and losing to the archive.
- A repeat archive of an already archived workspace no longer wipes the
  agents the earlier archive saved for undo.
- Undo no longer brings back an agent that was archived before the
  workspace archive and only loaded to read its history.
- Each local archive or undo request owns its own intent token, so a
  late response to an earlier request cannot release a newer request's
  hold on the row. An archive canceled by another client's undo puts the
  row back.
- The undo failure toast shows translated copy; the cause goes to the log.

docs/agent-lifecycle.md

@@ -270,6 +270,9 @@ The daemon runs one archive lane per workspace, shared by every connection
 | an undo runs: archive    | waits for the undo, then archives                         |
 | an undo runs: undo       | joins the running undo                                    |
 
+A request takes its place in the lane before its first `await`. Arrival order decides, so an undo
+sent right behind its archive still cancels it.
+
 An aborted archive stops at its next checkpoint and reports `canceled`; the undo unarchives only
 the agents that archive itself archived. Deleting the worktree directory is the point of no
 return: an undo after it recreates the worktree through workspace recovery. The client shows or