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

server/websocket.js

@@ -121,6 +121,9 @@ function initPtyWebSocket(server) {
     try {
       attach(ws, runId, size || { cols: 80, rows: 24 });
     } catch (err) {
+      // The browser only sees a socket that closed and retries every 1.5 s;
+      // this line is the one place that says why.
+      console.warn(`[WS] attach ${runId} failed:`, err.message);
       try {
         ws.close(1008, err.message);
       } catch {