Add Command Center v2: DQ/RAG integration, S3 browser, Jupyter, GPU matrix.

Mirror mo/atc-GPU layout with config/, docs/, scripts/ for Gitea deploy.

src/components/ThemeToggle.tsx

@@ -0,0 +1,23 @@
+import { useTheme } from '../context/ThemeContext'
+
+export function ThemeToggle() {
+  const { theme, toggle } = useTheme()
+  const isDark = theme === 'dark'
+
+  return (
+    <button
+      type="button"
+      onClick={toggle}
+      className="theme-toggle"
+      aria-label={isDark ? 'Switch to light mode' : 'Switch to dark mode'}
+      title={isDark ? 'Light mode' : 'Dark mode'}
+    >
+      <span className={`theme-toggle-track ${isDark ? 'is-dark' : ''}`}>
+        <span className="theme-toggle-thumb">{isDark ? '🌙' : '☀️'}</span>
+      </span>
+      <span className="text-xs font-mono hidden sm:inline text-[var(--text-muted)]">
+        {isDark ? 'Dark' : 'Light'}
+      </span>
+    </button>
+  )
+}