Add emoji confetti bursts and component playground.

Support app.relay.emoji_confetti on jumbo emoji clicks with canvas physics,
per-emoji particle profiles, and a fixed overlay that does not affect scroll.
Also add a Vite playground for live component previews and theme hover preview.

src/app/pages/ThemeManager.tsx

@@ -5,7 +5,7 @@ import {
   LightTheme,
   ThemeContextProvider,
   ThemeKind,
-  useActiveTheme,
+  useDisplayTheme,
   useSystemThemeKind,
 } from '../hooks/useTheme';
 import { useSetting } from '../state/hooks/settings';
@@ -29,21 +29,21 @@ export function UnAuthRouteThemeManager() {
 }
 
 export function AuthRouteThemeManager({ children }: { children: ReactNode }) {
-  const activeTheme = useActiveTheme();
+  const displayTheme = useDisplayTheme();
   const [monochromeMode] = useSetting(settingsAtom, 'monochromeMode');
 
   useEffect(() => {
     document.body.className = '';
     document.body.classList.add(configClass, varsClass);
 
-    document.body.classList.add(...activeTheme.classNames);
+    document.body.classList.add(...displayTheme.classNames);
 
     if (monochromeMode) {
       document.body.style.filter = 'grayscale(1)';
     } else {
       document.body.style.filter = '';
     }
-  }, [activeTheme, monochromeMode]);
+  }, [displayTheme, monochromeMode]);
 
-  return <ThemeContextProvider value={activeTheme}>{children}</ThemeContextProvider>;
+  return <ThemeContextProvider value={displayTheme}>{children}</ThemeContextProvider>;
 }