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/pty-attach.js

@@ -48,7 +48,7 @@ function attach(ws, runId, { cols, rows }) {
   } catch {
     /* session gone or tmux unavailable — attach below will surface that */
   }
-  const pty = spawnImpl("tmux", ["attach-session", "-t", runId], {
+  const pty = spawnImpl("tmux", ["attach-session", "-t", `=${runId}`], {
     name: "xterm-256color",
     cols: cols || 80,
     rows: rows || 24,