Fix: PWA loading screen now only shows on app startup, not on every navigation

Changed splash screen to use sessionStorage to detect first load vs navigation.
- Loading screen hidden by default, only shown on initial app load
- Uses sessionStorage flag to persist across navigation within same session
- Prevents jarring loading screen on every page navigation
- Updated hideLoadingScreen to use display:none instead of remove()

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

LittleShop/wwwroot/js/pwa.js

@@ -45,14 +45,14 @@ class PWAManager {
 
     hideLoadingScreen() {
         const loadingScreen = document.getElementById('pwa-loading-screen');
-        if (loadingScreen) {
+        if (loadingScreen && loadingScreen.style.display !== 'none') {
             // Add fade-out class
             loadingScreen.classList.add('fade-out');
 
-            // Remove from DOM after animation completes
+            // Hide after animation completes (don't remove from DOM to avoid layout issues)
             setTimeout(() => {
-                loadingScreen.remove();
-                console.log('PWA: Loading screen removed');
+                loadingScreen.style.display = 'none';
+                console.log('PWA: Loading screen hidden');
             }, 500);
         }
     }
@@ -701,15 +701,15 @@ window.addEventListener('load', () => {
     }
 });
 
-// Fallback: Ensure loading screen is removed after maximum timeout
+// Fallback: Ensure loading screen is hidden after maximum timeout
 // This guarantees the loading screen won't stay visible indefinitely
 setTimeout(() => {
     const loadingScreen = document.getElementById('pwa-loading-screen');
-    if (loadingScreen) {
-        console.log('PWA: Removing loading screen via fallback timeout');
+    if (loadingScreen && loadingScreen.style.display !== 'none') {
+        console.log('PWA: Hiding loading screen via fallback timeout');
         loadingScreen.classList.add('fade-out');
         setTimeout(() => {
-            loadingScreen.remove();
+            loadingScreen.style.display = 'none';
         }, 500);
     }
 }, 5000); // 5 second maximum