feat(ui): self-host fonts, remove Google Fonts CDN

- Bundle Satoshi (sans) and JetBrains Mono in web/fonts/
- New fonts.css with @font-face declarations
- Remove Google Fonts preconnect and stylesheet link
- Update --sans token: Satoshi replaces Space Grotesk/Inter
- Zero external font requests, works fully offline
- Keep extra fonts (Geo, Mooli, StackSansNotch) for future use

web/fonts.css

@@ -0,0 +1,67 @@
+/* ── Self-hosted fonts ─────────────────────────────── */
+
+/* Satoshi — primary sans */
+@font-face {
+    font-family: 'Satoshi';
+    src: url('/fonts/Satoshi-Light.woff2') format('woff2');
+    font-weight: 300;
+    font-style: normal;
+    font-display: swap;
+}
+
+@font-face {
+    font-family: 'Satoshi';
+    src: url('/fonts/Satoshi-Regular.woff2') format('woff2');
+    font-weight: 400;
+    font-style: normal;
+    font-display: swap;
+}
+
+@font-face {
+    font-family: 'Satoshi';
+    src: url('/fonts/Satoshi-Medium.woff2') format('woff2');
+    font-weight: 500;
+    font-style: normal;
+    font-display: swap;
+}
+
+@font-face {
+    font-family: 'Satoshi';
+    src: url('/fonts/Satoshi-Bold.woff2') format('woff2');
+    font-weight: 700;
+    font-style: normal;
+    font-display: swap;
+}
+
+/* JetBrains Mono — mono */
+@font-face {
+    font-family: 'JetBrains Mono';
+    src: url('/fonts/JetBrainsMono-Light.woff2') format('woff2');
+    font-weight: 300;
+    font-style: normal;
+    font-display: swap;
+}
+
+@font-face {
+    font-family: 'JetBrains Mono';
+    src: url('/fonts/JetBrainsMono-Regular.woff2') format('woff2');
+    font-weight: 400;
+    font-style: normal;
+    font-display: swap;
+}
+
+@font-face {
+    font-family: 'JetBrains Mono';
+    src: url('/fonts/JetBrainsMono-Medium.woff2') format('woff2');
+    font-weight: 500;
+    font-style: normal;
+    font-display: swap;
+}
+
+@font-face {
+    font-family: 'JetBrains Mono';
+    src: url('/fonts/JetBrainsMono-Bold.woff2') format('woff2');
+    font-weight: 700;
+    font-style: normal;
+    font-display: swap;
+}