feat: add splash screen with logo on app load and after login

- Show sofarr logo splash screen while app initialises
- On page load: splash stays visible while checking auth and fetching data
- After login: splash reappears while fetching initial downloads
- Minimum 1.2s display with smooth fade-out transition
- Subtle pulse animation on the logo

public/style.css

@@ -1,3 +1,34 @@
+/* ===== Splash Screen ===== */
+.splash-screen {
+  position: fixed;
+  top: 0;
+  left: 0;
+  width: 100%;
+  height: 100%;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  background: #f8f9fa;
+  z-index: 9999;
+  opacity: 1;
+  transition: opacity 0.4s ease-out;
+}
+
+.splash-screen.fade-out {
+  opacity: 0;
+}
+
+.splash-logo {
+  max-width: 280px;
+  width: 60%;
+  animation: splashPulse 1.8s ease-in-out infinite;
+}
+
+@keyframes splashPulse {
+  0%, 100% { transform: scale(1); opacity: 1; }
+  50% { transform: scale(1.03); opacity: 0.85; }
+}
+
 /* ===== Theme Variables ===== */
 :root, [data-theme="light"] {
   --bg-gradient-start: #667eea;