Enhance loading screen with animation and splash improvements

Updated the loading screen to include animated gold lines, a loader, and a spark effect. Adjusted splash visibility to ensure a minimum display time of 3 seconds and improved transitions for smoother visuals. Enhanced style and structure for better user experience during app initialization.

frontend/src/main.jsx

@@ -5,7 +5,7 @@ import { applyTheme, DEFAULT_THEME_KEY } from "./styles/themes";
 import { registerSW } from "virtual:pwa-register";
 
 async function bootstrap() {
-  // ✅ Theme sofort setzen
+  // Theme sofort setzen
   try {
     const key = localStorage.getItem("hpTheme:guest") || DEFAULT_THEME_KEY;
     applyTheme(key);
@@ -13,29 +13,37 @@ async function bootstrap() {
     applyTheme(DEFAULT_THEME_KEY);
   }
 
-  // ✅ Fonts abwarten (kein Layout-Jump)
+  // Fonts abwarten (verhindert Layout-Sprung)
   try {
     if (document.fonts?.ready) {
       await document.fonts.ready;
     }
   } catch {}
 
-  // React rendern
+  // App rendern
   ReactDOM.createRoot(document.getElementById("root")).render(<App />);
 
-  // ✅ Splash sauber ausblenden (KEIN Schwarz)
-  const splash = document.getElementById("app-splash");
-  if (splash) {
-    requestAnimationFrame(() => splash.classList.add("hide"));
-    setTimeout(() => splash.remove(), 220);
-  }
+  // Splash mind. 3 Sekunden anzeigen (3000ms)
+  const MIN_SPLASH_MS = 3000;
+  const tStart = performance.now();
 
-  // ✅ Service Worker ohne Reload-Flash
+  const hideSplash = () => {
+    const splash = document.getElementById("app-splash");
+    if (!splash) return;
+    splash.classList.add("hide");
+    setTimeout(() => splash.remove(), 320);
+  };
+
+  const elapsed = performance.now() - tStart;
+  const remaining = Math.max(0, MIN_SPLASH_MS - elapsed);
+  setTimeout(hideSplash, remaining);
+
+  // Service Worker ohne Auto-Reload-Flash
   registerSW({
     immediate: true,
     onNeedRefresh() {
       console.info("Neue Version verfügbar");
-      // später Toast möglich
+      // optional: später Toast "Update verfügbar"
     },
   });
 }