fix(calls): opaque backdrop for the PiP call window (#224)

The fork renders EC transparent so the room wallpaper shows through the
full-size embed; in PiP the element behind the frame is whatever room you
navigated to, so the timeline bled through the participant tiles. The PiP
container now gets the surface colour (the full embed keeps the wallpaper).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/components/CallEmbedProvider.tsx

@@ -1231,7 +1231,15 @@ export function CallEmbedProvider({ children }: CallEmbedProviderProps) {
           left: 0,
           width: '100%',
           height: '50%',
-          ...(callVisible && !pipMode ? wallpaperStyle : {}),
+          // [Gitea #224] The fork renders EC transparent (lotusTransparent) so the
+          // wallpaper shows through the full-size embed; in PiP the thing behind
+          // the frame is whatever room you navigated to, so give it an opaque
+          // surface instead of letting the timeline bleed through the tiles.
+          ...(pipMode
+            ? { background: color.Surface.Container }
+            : callVisible
+              ? wallpaperStyle
+              : {}),
         }}
         ref={callEmbedRef}
       >