Add Export APIs & Optimization Checks (Phases 14-15)

Features Added:
- HAR file export endpoint (/api/export/:testId/har)
- CSV metrics export endpoint (/api/export/:testId/csv)
- Optimization checker analyzing 8 categories:
  * Image optimization
  * Text compression (gzip/brotli)
  * Cache policies
  * Render-blocking resources
  * Unused JavaScript
  * Unused CSS
  * HTTP/2 adoption
  * Code minification
- Frontend optimization checklist with color-coded warnings
- Export buttons integrated into results UI

Technical Implementation:
- Created lib/optimization-checker.js with Lighthouse audit analysis
- Added optimization score calculation (0-100%)
- Potential time savings displayed for each check
- Export buttons wired to download endpoints
- Optimization data saved alongside each test result

lib/optimization-checker.js

@@ -0,0 +1,134 @@
+/**
+ * Optimization Checker
+ * Analyzes Lighthouse results and provides actionable recommendations
+ */
+
+function analyzeOptimizations(lighthouseResult) {
+    const audits = lighthouseResult.audits;
+    const checks = [];
+    
+    // 1. Image Optimization
+    const unoptimizedImages = audits['uses-optimized-images'];
+    if (unoptimizedImages && unoptimizedImages.score < 1) {
+        checks.push({
+            category: 'Images',
+            status: 'warning',
+            title: 'Unoptimized Images Detected',
+            description: `${unoptimizedImages.details?.items?.length || 0} images could be optimized`,
+            savings: unoptimizedImages.numericValue || 0,
+            impact: 'high'
+        });
+    }
+    
+    // 2. Text Compression
+    const textCompression = audits['uses-text-compression'];
+    if (textCompression && textCompression.score < 1) {
+        checks.push({
+            category: 'Compression',
+            status: 'warning',
+            title: 'Enable Text Compression',
+            description: 'Text resources not served with compression (gzip/brotli)',
+            savings: textCompression.numericValue || 0,
+            impact: 'medium'
+        });
+    }
+    
+    // 3. Cache Policy
+    const cachePolicy = audits['uses-long-cache-ttl'];
+    if (cachePolicy && cachePolicy.score < 0.9) {
+        checks.push({
+            category: 'Caching',
+            status: 'info',
+            title: 'Serve Static Assets with Efficient Cache Policy',
+            description: `${cachePolicy.details?.items?.length || 0} resources have low cache TTL`,
+            savings: cachePolicy.numericValue || 0,
+            impact: 'medium'
+        });
+    }
+    
+    // 4. Render-Blocking Resources
+    const renderBlocking = audits['render-blocking-resources'];
+    if (renderBlocking && renderBlocking.score < 1) {
+        checks.push({
+            category: 'Performance',
+            status: 'error',
+            title: 'Eliminate Render-Blocking Resources',
+            description: `${renderBlocking.details?.items?.length || 0} render-blocking  resources found`,
+            savings: renderBlocking.numericValue || 0,
+            impact: 'high'
+        });
+    }
+    
+    // 5. Unused JavaScript
+    const unusedJS = audits['unused-javascript'];
+    if (unusedJS && unusedJS.score < 0.9) {
+        checks.push({
+            category: 'JavaScript',
+            status: 'warning',
+            title: 'Reduce Unused JavaScript',
+            description: 'Defer or remove unused JS code',
+            savings: unusedJS.numericValue || 0,
+            impact: 'high'
+        });
+    }
+    
+    // 6. Unused CSS
+    const unusedCSS = audits['unused-css-rules'];
+    if (unusedCSS && unusedCSS.score < 0.9) {
+        checks.push({
+            category: 'CSS',
+            status: 'warning',
+            title: 'Remove Unused CSS',
+            description: 'Defer or remove unused CSS rules',
+            savings: unusedCSS.numericValue || 0,
+            impact: 'medium'
+        });
+    }
+    
+    // 7. HTTP/2
+    const http2 = audits['uses-http2'];
+    if (http2 && http2.score < 1) {
+        checks.push({
+            category: 'Protocol',
+            status: 'info',
+            title: 'Use HTTP/2',
+            description: 'Serve resources over HTTP/2 for better performance',
+            impact: 'medium'
+        });
+    }
+    
+    // 8. Minification
+    const minifyCSS = audits['unminified-css'];
+    const minifyJS = audits['unminified-javascript'];
+    if ((minifyCSS && minifyCSS.score < 1) || (minifyJS && minifyJS.score < 1)) {
+        checks.push({
+            category: 'Minification',
+            status: 'warning',
+            title: 'Minify CSS and JavaScript',
+            description: 'Minify code to reduce file sizes',
+            savings: (minifyCSS?.numericValue || 0) + (minifyJS?.numericValue || 0),
+            impact: 'medium'
+        });
+    }
+    
+    // Calculate overall optimization score
+    const totalChecks = 8;
+    const passed = checks.filter(c => c.status === 'success').length;
+    const warnings = checks.filter(c => c.status === 'warning').length;
+    const errors = checks.filter(c => c.status === 'error').length;
+    
+    return {
+        checks,
+        summary: {
+            totalChecks,
+            passed: totalChecks - checks.length,
+            warnings,
+            errors,
+            score: Math.round(((totalChecks - checks.length) / totalChecks) * 100)
+        }
+    };
+}
+
+module.exports = {
+    analyzeOptimizations
+};