Implement M1.5 visual design foundation: tokens, IBM Plex, theme toggle, chart themes

docs/architecture/01-state-and-stores.md

@@ -373,8 +373,8 @@ export function ThemeToggle() {
   const theme = useAppStore((s) => s.uiTheme);
   const setTheme = useAppStore((s) => s.setTheme);
   return (
-    <button onClick={() => setTheme(theme === 'experimental' ? 'light' : 'experimental')}>
-      {theme === 'experimental' ? '🌙' : '☀️'}
+    <button onClick={() => setTheme(theme === 'dark' ? 'light' : 'dark')}>
+      {theme === 'dark' ? '🌙' : '☀️'}
     </button>
   );
 }