feat: add PWA support with service worker and update prompt

- Updated package.json to include vite-plugin-pwa and workbox-window.
- Added icon SVGs for PWA: icon-512.svg and maskable-512.svg.
- Created a manifest.json for PWA configuration.
- Implemented PwaUpdatePrompt component to notify users of available updates.
- Enhanced CookieConsent and SiteAssistant components for better layout and responsiveness.
- Updated global CSS for safe-area insets and mobile-first enhancements.
- Registered service worker in usePwaRegistration hook for managing updates.
- Modified Vite configuration to integrate PWA features and caching strategies.

frontend/public/icons/icon-512.svg

@@ -0,0 +1,13 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" fill="none">
+  <defs>
+    <linearGradient id="bg" x1="0" y1="0" x2="512" y2="512" gradientUnits="userSpaceOnUse">
+      <stop offset="0%" stop-color="#4F46E5"/>
+      <stop offset="100%" stop-color="#7C3AED"/>
+    </linearGradient>
+  </defs>
+  <rect width="512" height="512" rx="112" fill="url(#bg)"/>
+  <path d="M160 128h112l80 80v176a16 16 0 0 1-16 16H160a16 16 0 0 1-16-16V144a16 16 0 0 1 16-16z" fill="rgba(255,255,255,0.15)" stroke="#fff" stroke-width="16"/>
+  <path d="M272 128v64a16 16 0 0 0 16 16h64" stroke="#fff" stroke-width="16" fill="none"/>
+  <path d="M192 256h128M192 296h96M192 336h64" stroke="#93C5FD" stroke-width="14" stroke-linecap="round"/>
+  <text x="312" y="432" font-family="Arial,Helvetica,sans-serif" font-weight="700" font-size="128" fill="#E0E7FF" opacity="0.6">D</text>
+</svg>

frontend/public/icons/maskable-512.svg

@@ -0,0 +1,16 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" fill="none">
+  <!-- Maskable icon: safe zone is central 80% (409.6px), so content fits within ~51-461 -->
+  <defs>
+    <linearGradient id="bg" x1="0" y1="0" x2="512" y2="512" gradientUnits="userSpaceOnUse">
+      <stop offset="0%" stop-color="#4F46E5"/>
+      <stop offset="100%" stop-color="#7C3AED"/>
+    </linearGradient>
+  </defs>
+  <!-- Full bleed background -->
+  <rect width="512" height="512" fill="url(#bg)"/>
+  <!-- Content centered within safe zone -->
+  <path d="M176 144h96l72 72v160a14 14 0 0 1-14 14H176a14 14 0 0 1-14-14V158a14 14 0 0 1 14-14z" fill="rgba(255,255,255,0.15)" stroke="#fff" stroke-width="14"/>
+  <path d="M272 144v56a14 14 0 0 0 14 14h56" stroke="#fff" stroke-width="14" fill="none"/>
+  <path d="M204 264h112M204 300h84M204 336h56" stroke="#93C5FD" stroke-width="12" stroke-linecap="round"/>
+  <text x="296" y="416" font-family="Arial,Helvetica,sans-serif" font-weight="700" font-size="112" fill="#E0E7FF" opacity="0.6">D</text>
+</svg>

frontend/public/manifest.json

@@ -0,0 +1,57 @@
+{
+  "name": "Dociva — Free Online File Tools",
+  "short_name": "Dociva",
+  "description": "30+ free tools: merge, split, compress, convert PDFs, images, videos & text. No signup required.",
+  "start_url": "/",
+  "id": "/",
+  "display": "standalone",
+  "background_color": "#ffffff",
+  "theme_color": "#2563eb",
+  "orientation": "any",
+  "scope": "/",
+  "categories": ["productivity", "utilities"],
+  "dir": "auto",
+  "lang": "en",
+  "prefer_related_applications": false,
+  "icons": [
+    {
+      "src": "/favicon.svg",
+      "sizes": "any",
+      "type": "image/svg+xml",
+      "purpose": "any"
+    },
+    {
+      "src": "/icons/icon-512.svg",
+      "sizes": "512x512",
+      "type": "image/svg+xml",
+      "purpose": "any"
+    },
+    {
+      "src": "/icons/maskable-512.svg",
+      "sizes": "512x512",
+      "type": "image/svg+xml",
+      "purpose": "maskable"
+    }
+  ],
+  "screenshots": [],
+  "shortcuts": [
+    {
+      "name": "Compress PDF",
+      "short_name": "Compress",
+      "url": "/compress-pdf",
+      "icons": [{ "src": "/favicon.svg", "sizes": "any", "type": "image/svg+xml" }]
+    },
+    {
+      "name": "Merge PDF",
+      "short_name": "Merge",
+      "url": "/merge-pdf",
+      "icons": [{ "src": "/favicon.svg", "sizes": "any", "type": "image/svg+xml" }]
+    },
+    {
+      "name": "Convert to PDF",
+      "short_name": "Convert",
+      "url": "/image-to-pdf",
+      "icons": [{ "src": "/favicon.svg", "sizes": "any", "type": "image/svg+xml" }]
+    }
+  ]
+}