feat: Add dynamic Open Graph image generation with correct aspect ratio

- Create /api/og-image endpoint that generates SVG with 1.91:1 ratio (1200x630px)
- Prevents logo cropping on Facebook and Twitter
- Uses safe padding (150px) to ensure content is never cut off
- Update default OG image to use dynamic endpoint
- Add SEO testing documentation

app/api/og-image/route.ts

@@ -0,0 +1,78 @@
+import { NextResponse } from 'next/server';
+import { config } from '@/lib/config';
+import { getBaseUrl } from '@/lib/seo';
+import { headers } from 'next/headers';
+
+export const dynamic = 'force-dynamic';
+export const runtime = 'nodejs';
+
+/**
+ * Generate Open Graph image as SVG with correct aspect ratio (1.91:1 = 1200x630)
+ * This prevents cropping on Facebook and Twitter
+ */
+export async function GET() {
+    const baseUrl = await getBaseUrl();
+    const appName = config.appName;
+    const bgColor = config.colors.backgroundColor || '#ffffff';
+    const primaryColor = config.colors.themeColor || '#000000';
+    
+    // SVG with correct Open Graph dimensions: 1200x630 (1.91:1 ratio)
+    // Safe area: 150px padding on all sides to prevent cropping
+    // This ensures content is never cut off on Facebook/Twitter
+    const svg = `<?xml version="1.0" encoding="UTF-8"?>
+<svg width="1200" height="630" xmlns="http://www.w3.org/2000/svg">
+  <!-- Background -->
+  <rect width="1200" height="630" fill="${bgColor}"/>
+  
+  <!-- Gradient definition -->
+  <defs>
+    <linearGradient id="gradient" x1="0%" y1="0%" x2="100%" y2="0%">
+      <stop offset="0%" style="stop-color:#667eea;stop-opacity:1" />
+      <stop offset="50%" style="stop-color:#764ba2;stop-opacity:1" />
+      <stop offset="100%" style="stop-color:#06b6d4;stop-opacity:1" />
+    </linearGradient>
+  </defs>
+  
+  <!-- Content container - centered with safe padding (150px on all sides) -->
+  <g transform="translate(150, 150)">
+    <!-- Main graphic area (centered horizontally) -->
+    <g transform="translate(300, 0)">
+      <!-- Musical note (left side, within safe area) -->
+      <g fill="url(#gradient)" opacity="0.9">
+        <!-- Note head -->
+        <ellipse cx="0" cy="40" rx="40" ry="28"/>
+        <!-- Note stem -->
+        <rect x="30" y="-60" width="16" height="100" rx="2"/>
+      </g>
+      
+      <!-- Waveform (center-right, within safe area) -->
+      <g transform="translate(70, 15)" fill="none" stroke="url(#gradient)" stroke-width="8" stroke-linecap="round" opacity="0.8">
+        <path d="M 0 25 Q 20 -15 40 25 T 80 25"/>
+        <path d="M 0 40 Q 20 0 40 40 T 80 40"/>
+        <path d="M 0 55 Q 20 15 40 55 T 80 55"/>
+      </g>
+      
+      <!-- Vertical bar (right side, within safe area) -->
+      <rect x="170" y="0" width="10" height="120" fill="url(#gradient)" opacity="0.7" rx="5"/>
+    </g>
+    
+    <!-- App name (centered, within safe vertical area) -->
+    <text x="450" y="180" font-family="system-ui, -apple-system, sans-serif" font-size="56" font-weight="bold" fill="${primaryColor}" text-anchor="middle" letter-spacing="-0.5">
+      ${appName}
+    </text>
+    
+    <!-- Domain/subtitle (centered, within safe vertical area) -->
+    <text x="450" y="220" font-family="system-ui, -apple-system, sans-serif" font-size="28" fill="#666666" text-anchor="middle">
+      ${config.domain}
+    </text>
+  </g>
+</svg>`;
+
+    return new NextResponse(svg, {
+        headers: {
+            'Content-Type': 'image/svg+xml',
+            'Cache-Control': 'public, max-age=3600, s-maxage=3600',
+        },
+    });
+}
+