feat: show encoder implementation in Connection Info, VP9 recommended hint

- Connection Info now shows encoder impl (e.g. libvpx, OpenH264,
  ExternalEncoder) on send-side video tracks alongside quality
  limitation reason
- Amber warning "VP9 is recommended" when H.264 is selected

packages/web/src/components/voice/ScreenShareSettingsPopover.tsx

@@ -199,6 +199,11 @@ export function ScreenShareSettingsPopover({ open, onClose, anchorRef }: ScreenS
               </button>
             ))}
           </div>
+          {config.codec !== 'vp9' && (
+            <div className="text-[10px] text-accent-amber/80 mt-1">
+              VP9 is recommended for most setups
+            </div>
+          )}
         </div>
 
         {/* Bitrate Override */}