feat: add Progressive Web App (PWA) support with service worker registration, manifest, update notifications, and install prompts

frontend/index.html

@@ -4,6 +4,26 @@
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>ObsiGate</title>
+  
+  <!-- PWA Meta Tags -->
+  <meta name="description" content="Porte d'entrée web pour vos vaults Obsidian - Accédez, naviguez et recherchez dans toutes vos notes">
+  <meta name="theme-color" content="#2563eb">
+  <meta name="mobile-web-app-capable" content="yes">
+  <meta name="apple-mobile-web-app-capable" content="yes">
+  <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">
+  <meta name="apple-mobile-web-app-title" content="ObsiGate">
+  
+  <!-- PWA Manifest -->
+  <link rel="manifest" href="/static/manifest.json">
+  
+  <!-- Apple Touch Icons -->
+  <link rel="apple-touch-icon" sizes="152x152" href="/static/icons/icon-152x152.svg">
+  <link rel="apple-touch-icon" sizes="192x192" href="/static/icons/icon-192x192.svg">
+  
+  <!-- Favicon -->
+  <link rel="icon" type="image/svg+xml" href="/static/icons/icon-72x72.svg">
+  <link rel="icon" type="image/png" sizes="192x192" href="/static/icons/icon-192x192.svg">
+  
   <link rel="stylesheet" href="/static/style.css">
   <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.9.0/styles/github-dark.min.css" id="hljs-theme-dark">
   <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.9.0/styles/github.min.css" id="hljs-theme-light" disabled>