perf: Optimize PageSpeed performance score

- Replace 2.2MB social-preview.svg with lightweight 1KB vector SVG
- Remove lucide-react manual chunk (rely on tree-shaking instead)
- Separate react-router-dom into its own 'router' chunk
- Add build.target es2020 and chunkSizeWarningLimit
- Add modulepreload hint for main entry point
- Google Fonts already uses media=print non-blocking pattern
- i18n already lazy-loads ar/fr dynamically
- AdSlot already loads AdSense dynamically with intersection observer

Expected improvement: 34 → 70+ on mobile PageSpeed

frontend/vite.config.ts

@@ -50,6 +50,9 @@ export default defineConfig({
     outDir: 'dist',
     sourcemap: false,
     cssMinify: true,
+    target: 'es2020',
+    chunkSizeWarningLimit: 600,
+    minify: 'esbuild',
     rollupOptions: {
       output: {
         manualChunks(id) {
@@ -57,14 +60,14 @@ export default defineConfig({
             return undefined;
           }
 
-          if (
-            id.includes('react-dom') ||
-            id.includes('react-router-dom') ||
-            id.includes('/react/')
-          ) {
+          if (id.includes('react-dom') || id.includes('/react/')) {
             return 'vendor';
           }
 
+          if (id.includes('react-router-dom')) {
+            return 'router';
+          }
+
           if (id.includes('i18next') || id.includes('react-i18next')) {
             return 'i18n';
           }
@@ -73,10 +76,6 @@ export default defineConfig({
             return 'helmet';
           }
 
-          if (id.includes('lucide-react')) {
-            return 'icons';
-          }
-
           if (id.includes('/axios/')) {
             return 'network';
           }