fix: terminal WebSocket connection — manage xterm containers in JS

- Remove Alpine x-for template for xterm containers (async rendering bug)
- Add static #xterm-wrapper div, JS creates/removes container elements directly
- addTab() uses document.createElement + appendChild for instant DOM
- switchTab() toggles display:block/none, closeTab() removes from DOM
- Add console.log for WebSocket open/close/error debugging
- Terminal now connects on page load

app/backend/static/css/output.css

@@ -369,6 +369,9 @@
   .block {
     display: block;
   }
+  .contents {
+    display: contents;
+  }
   .flex {
     display: flex;
   }