Add comprehensive favicon and PWA support

assets/images/apple-touch-icon.svg

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+<svg width="180" height="180" xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <linearGradient id="appleIconGrad" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" style="stop-color:#667eea;stop-opacity:1" />
+      <stop offset="100%" style="stop-color:#764ba2;stop-opacity:1" />
+    </linearGradient>
+  </defs>
+  <!-- Apple touch icon background -->
+  <rect width="180" height="180" fill="url(#appleIconGrad)" rx="30"/>
+  
+  <!-- UK Data Services logo -->
+  <text x="90" y="110" font-family="Arial, sans-serif" font-size="48" font-weight="bold" fill="white" text-anchor="middle">UK</text>
+  <text x="90" y="140" font-family="Arial, sans-serif" font-size="16" font-weight="normal" fill="white" text-anchor="middle" opacity="0.9">DATA SERVICES</text>
+  
+  <!-- Data visualization elements -->
+  <rect x="30" y="40" width="120" height="8" fill="white" opacity="0.7" rx="4"/>
+  <rect x="40" y="55" width="100" height="6" fill="white" opacity="0.6" rx="3"/>
+  <rect x="35" y="70" width="110" height="4" fill="white" opacity="0.5" rx="2"/>
+  
+  <!-- Corner accent -->
+  <circle cx="150" cy="45" r="15" fill="white" opacity="0.3"/>
+  <circle cx="45" cy="150" r="12" fill="white" opacity="0.2"/>
+</svg>

assets/images/favicon-16x16.svg

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+<svg width="16" height="16" xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <linearGradient id="faviconGrad16" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" style="stop-color:#667eea;stop-opacity:1" />
+      <stop offset="100%" style="stop-color:#764ba2;stop-opacity:1" />
+    </linearGradient>
+  </defs>
+  <!-- Favicon background -->
+  <rect width="16" height="16" fill="url(#faviconGrad16)" rx="3"/>
+  <!-- Simplified UK initials for small size -->
+  <text x="8" y="12" font-family="Arial, sans-serif" font-size="8" font-weight="bold" fill="white" text-anchor="middle">UK</text>
+</svg>

assets/images/favicon-32x32.svg

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+<svg width="32" height="32" xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <linearGradient id="faviconGrad32" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" style="stop-color:#667eea;stop-opacity:1" />
+      <stop offset="100%" style="stop-color:#764ba2;stop-opacity:1" />
+    </linearGradient>
+  </defs>
+  <!-- Favicon background -->
+  <rect width="32" height="32" fill="url(#faviconGrad32)" rx="6"/>
+  <!-- UK initials -->
+  <text x="16" y="22" font-family="Arial, sans-serif" font-size="16" font-weight="bold" fill="white" text-anchor="middle">UK</text>
+  <!-- Data symbol -->
+  <rect x="6" y="6" width="20" height="2" fill="white" opacity="0.8" rx="1"/>
+  <rect x="8" y="9" width="16" height="1" fill="white" opacity="0.6" rx="0.5"/>
+</svg>