feat: fix favicon implementation for Google search and PWA support

- Add background to favicon.svg (RGB 38,45,59)
- Generate all required PNG sizes (192x192, 512x512, 180x180)
- Create site.webmanifest with proper PWA config
- Standardize favicon links across 116 HTML files
- Fix incorrect MIME types in 50+ pages

public/site.webmanifest

@@ -0,0 +1,45 @@
+{
+    "name": "BentoPDF",
+    "short_name": "BentoPDF",
+    "description": "Free online PDF tools - Privacy-first PDF toolkit that works 100% in your browser",
+    "start_url": "/",
+    "display": "standalone",
+    "background_color": "#262d3b",
+    "theme_color": "#4f46e5",
+    "orientation": "portrait-primary",
+    "icons": [
+        {
+            "src": "/images/favicon-192x192.png",
+            "sizes": "192x192",
+            "type": "image/png",
+            "purpose": "maskable any"
+        },
+        {
+            "src": "/images/favicon-512x512.png",
+            "sizes": "512x512",
+            "type": "image/png",
+            "purpose": "maskable any"
+        },
+        {
+            "src": "/images/apple-touch-icon.png",
+            "sizes": "180x180",
+            "type": "image/png",
+            "purpose": "any"
+        }
+    ],
+    "categories": [
+        "productivity",
+        "utilities",
+        "privacy",
+        "pdf",
+        "security",
+        "offline",
+        "tools"
+    ],
+    "screenshots": [],
+    "share_target": {
+        "action": "/",
+        "method": "GET",
+        "enctype": "application/x-www-form-urlencoded"
+    }
+}