fix: v2.5.8 — the browser terminal attaches on Windows

node-pty on Windows looks the file it starts up on PATH exactly as given and
never adds `.exe`, so `tmux attach-session` started as a bare `tmux` failed
with "File not found" on every attach: the browser's terminal socket opened,
closed, and reconnected every 1.5 s.

- pty-attach.js: attachBinary names tmux by its full file name on Windows
  (ai-tools.which("tmux"), else tmux.exe)
- websocket.js: an attach that throws is logged as `[WS] attach <run> failed`,
  the one place that says why the terminal keeps reconnecting

package.json

@@ -1,6 +1,6 @@
 {
   "name": "agenthub",
-  "version": "2.5.7",
+  "version": "2.5.8",
   "bin": {
     "agenthub": "bin/agenthub.js"
   },