feat: web UI on socket protocol 2 (step 2b)

The UI talks to the device over the one socket at /ws: the sync fills the
shade model, its events redraw the lists, and every read, command, edit,
setting, scan and reboot is an op. Only /loginContext, /login and the file
transfers stay on HTTP, so a page load opens no other connection.

- The 8080 socket, editJSON/requestResult and the /controller, /rooms,
  /shades, /groups, /room, /shade, /group, settings and command routes are
  no longer used by the UI.
- An edit's callback gets the item once its event is in (ProtoClient
  waitFor); busy edits and saves are sent again.
- The token is kept in sessionStorage. When /ws is refused and
  /loginContext says a login is needed, the client stops retrying and the
  login panel opens. Backup and uploads send the token.
- A banner shows when the device speaks another protocol version.
- Removed dead code: the /pairShade call and its unused /unpairShade twin,
  loadLogin, login.html (broken, linked from nowhere), Secure Config Only's
  checkbox (protocol 2 has two modes) and the HTTP helpers nothing uses.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

data-src/main.css

@@ -868,3 +868,14 @@ div.frame-pulses {
         padding-right:14px;
     }
 }
+/* Shown when the device speaks another protocol version than this page. */
+.version-banner {
+    position: sticky;
+    top: 0;
+    z-index: 100;
+    padding: 8px 12px;
+    background: orangered;
+    color: white;
+    font-size: 14px;
+    text-align: center;
+}