feat: Implement comprehensive PWA functionality

- Add full PWA configuration with manifest and service worker
- Create PWAInstallBanner component with mobile detection
- Implement install banner on login page (shows below login form)
- Add usePWA composable for reusable PWA functionality
- Configure offline support with Workbox caching strategies
- Add PWA initialization plugin
- Update app name to 'Port Nimara Portal' throughout
- Use circular logo in install banner and instructions
- Banner shows only once and hides if already installed
- Support both Android (direct install) and iOS (manual instructions)
- Add comprehensive documentation for PWA implementation

Features:
- Mobile-only install banner with dismissal tracking
- Standalone mode detection to hide banner when installed
- Platform-specific installation instructions
- Offline functionality with API caching
- Auto-updating service worker
- Native app-like experience when installed

plugins/pwa.client.ts

@@ -0,0 +1,16 @@
+export default defineNuxtPlugin(() => {
+  const { init } = usePWA();
+
+  // Initialize PWA functionality when the app starts
+  if (process.client) {
+    init();
+    
+    // Register service worker update handler
+    if ('serviceWorker' in navigator) {
+      navigator.serviceWorker.addEventListener('controllerchange', () => {
+        console.log('PWA updated successfully');
+        // You could show a toast notification here
+      });
+    }
+  }
+});