refactor(kon): add design tokens — radius scale, title size, button component classes

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

src/app.css

@@ -31,8 +31,20 @@
   --color-sidebar: #13120f;
   --color-nav-active: #201e1a;
   --color-hover: #1e1c18;
+
+  /* === Layout Tokens === */
+  --radius-sm: 6px;
+  --radius-md: 8px;
+  --radius-lg: 12px;
+  --radius-xl: 16px;
+  --title-size: 26px;
 }
 
+/* === Button Component Classes === */
+.btn-sm { @apply px-2.5 py-1 text-[11px]; }
+.btn-md { @apply px-3 py-1.5 text-[12px]; }
+.btn-lg { @apply px-4 py-2 text-[13px]; }
+
 /* === Light theme overrides === */
 html.light {
   --color-bg: #faf8f5;