Self-host fonts for improved performance

- Download JetBrains Mono and Pretendard fonts (woff2)
- Add fonts.css with @font-face declarations
- Remove Google Fonts external dependencies
- Update CSP to remove fonts.googleapis.com
- Update all HTML files to use local fonts

Improves FCP/LCP by eliminating external font requests.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

sla.html

@@ -9,9 +9,7 @@
   <link rel="stylesheet" href="style.css">
 
   <!-- Fonts -->
-  <link rel="preconnect" href="https://fonts.googleapis.com">
-  <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
-  <link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=JetBrains+Mono:wght@400;700&family=Pretendard:wght@400;600;700&display=swap">
+  <link rel="stylesheet" href="fonts.css">
 
   <!-- Favicon -->
   <link rel="icon" type="image/svg+xml" href="data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 100 100'><rect fill='%230ea5e9' rx='20' width='100' height='100'/><text x='50' y='70' font-size='60' text-anchor='middle' fill='white' font-family='sans-serif' font-weight='bold'>A</text></svg>">