fix(tmux,run,hooks): the four pre-existing bugs the #37 evaluation found

- tmux targets are exact (`=name`, `=name:` for panes/options): a bare
  `-t agenthub-lane-1` resolves by prefix to agenthub-lane-12 once lane 1
  is gone, so killing a finished lane could kill another.
- getRun/killRun refuse ids that are not `agenthub-lane-<n>`, so
  DELETE /api/run/main can no longer kill a user's own tmux session.
- router/apply reports restart_required only for a running pane; getRun
  returns a `gone` handle, so it was always true.
- needs_action is cleared only by the session that raised it (new nullable
  lanes.needs_action_session); a second session in the same cwd used to
  clear it on its second hook.

server/lib/lanes.js

@@ -69,6 +69,7 @@ const PATCHABLE = new Set([
   "gate_decision",
   "ci_status",
   "needs_action",
+  "needs_action_session",
   "links",
   "notes",
   "session_id",