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>

fonts.css

@@ -0,0 +1,44 @@
+/* JetBrains Mono - Regular (400) */
+@font-face {
+  font-family: 'JetBrains Mono';
+  font-style: normal;
+  font-weight: 400;
+  font-display: swap;
+  src: url('/fonts/jetbrains-mono-400.woff2') format('woff2');
+}
+
+/* JetBrains Mono - Bold (700) */
+@font-face {
+  font-family: 'JetBrains Mono';
+  font-style: normal;
+  font-weight: 700;
+  font-display: swap;
+  src: url('/fonts/jetbrains-mono-700.woff2') format('woff2');
+}
+
+/* Pretendard - Regular (400) */
+@font-face {
+  font-family: 'Pretendard';
+  font-style: normal;
+  font-weight: 400;
+  font-display: swap;
+  src: url('/fonts/pretendard-400.woff2') format('woff2');
+}
+
+/* Pretendard - SemiBold (600) */
+@font-face {
+  font-family: 'Pretendard';
+  font-style: normal;
+  font-weight: 600;
+  font-display: swap;
+  src: url('/fonts/pretendard-600.woff2') format('woff2');
+}
+
+/* Pretendard - Bold (700) */
+@font-face {
+  font-family: 'Pretendard';
+  font-style: normal;
+  font-weight: 700;
+  font-display: swap;
+  src: url('/fonts/pretendard-700.woff2') format('woff2');
+}