✨(frontend) add a basic control bar to the PiP window

The PiP control bar shares state with the main window's control
bar — most importantly, the reaction toolbar and the mic/camera
toggles, which are fully stateful.

Sharing state works naturally here because the PiP content is
rendered through a portal into the same React tree, so the
controls in both windows read from and write to the same stores.

Co-authored-by: Cyril <c.gromoff@gmail.com>

src/frontend/src/locales/en/rooms.json

@@ -236,7 +236,8 @@
       "title": "Your video call is in another window.",
       "description": "Picture-in-Picture mode allows you to stay connected to the call while performing other tasks.",
       "bringBack": "Bring the call back here"
-    }
+    },
+    "controlBar": "Meeting controls"
   },
   "options": {
     "buttonLabel": "More Options",