fix: self-host fonts instead of loading from Google Fonts CDN

Loading fonts from fonts.googleapis.com sends user IP addresses to
Google on every page load — a GDPR violation. Self-host DM Sans and
JetBrains Mono as woff2 files bundled with the UI.

- Download DM Sans (400/500/600/700 + 400 italic) woff2 files
- Download JetBrains Mono (400/500/600) woff2 files
- Replace @import url(googleapis) with local @font-face declarations
- Both fonts are OFL-licensed (free to self-host)
- Total size: ~135KB for all 8 font files

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/index.css

@@ -1,4 +1,62 @@
-@import url('https://fonts.googleapis.com/css2?family=DM+Sans:ital,opsz,wght@0,9..40,100..1000;1,9..40,100..1000&family=JetBrains+Mono:wght@400;500;600&display=swap');
+/* DM Sans — self-hosted (GDPR compliant) */
+@font-face {
+  font-family: 'DM Sans';
+  font-style: normal;
+  font-weight: 400;
+  font-display: swap;
+  src: url('./fonts/dm-sans-400.woff2') format('woff2');
+}
+@font-face {
+  font-family: 'DM Sans';
+  font-style: normal;
+  font-weight: 500;
+  font-display: swap;
+  src: url('./fonts/dm-sans-500.woff2') format('woff2');
+}
+@font-face {
+  font-family: 'DM Sans';
+  font-style: normal;
+  font-weight: 600;
+  font-display: swap;
+  src: url('./fonts/dm-sans-600.woff2') format('woff2');
+}
+@font-face {
+  font-family: 'DM Sans';
+  font-style: normal;
+  font-weight: 700;
+  font-display: swap;
+  src: url('./fonts/dm-sans-700.woff2') format('woff2');
+}
+@font-face {
+  font-family: 'DM Sans';
+  font-style: italic;
+  font-weight: 400;
+  font-display: swap;
+  src: url('./fonts/dm-sans-400-italic.woff2') format('woff2');
+}
+
+/* JetBrains Mono — self-hosted (GDPR compliant) */
+@font-face {
+  font-family: 'JetBrains Mono';
+  font-style: normal;
+  font-weight: 400;
+  font-display: swap;
+  src: url('./fonts/jetbrains-mono-400.woff2') format('woff2');
+}
+@font-face {
+  font-family: 'JetBrains Mono';
+  font-style: normal;
+  font-weight: 500;
+  font-display: swap;
+  src: url('./fonts/jetbrains-mono-500.woff2') format('woff2');
+}
+@font-face {
+  font-family: 'JetBrains Mono';
+  font-style: normal;
+  font-weight: 600;
+  font-display: swap;
+  src: url('./fonts/jetbrains-mono-600.woff2') format('woff2');
+}
 
 :root {
   font-family: 'DM Sans', system-ui, sans-serif;