add dashboard layout and routing

dashboard/src/components/layout/Sidebar.tsx

@@ -0,0 +1,35 @@
+import { NavLink } from 'react-router-dom';
+
+const navItems = [
+  { to: '/', label: 'Reviews', icon: '📋' },
+  { to: '/metrics', label: 'Metrics', icon: '📊' },
+];
+
+export function Sidebar() {
+  return (
+    <aside className="w-64 bg-white border-r border-gray-200 min-h-screen">
+      <nav className="p-4">
+        <ul className="space-y-1">
+          {navItems.map((item) => (
+            <li key={item.to}>
+              <NavLink
+                to={item.to}
+                end={item.to === '/'}
+                className={({ isActive }) =>
+                  `flex items-center gap-3 px-3 py-2 rounded-lg text-sm font-medium transition-colors ${
+                    isActive
+                      ? 'bg-indigo-50 text-indigo-700'
+                      : 'text-gray-700 hover:bg-gray-100'
+                  }`
+                }
+              >
+                <span>{item.icon}</span>
+                <span>{item.label}</span>
+              </NavLink>
+            </li>
+          ))}
+        </ul>
+      </nav>
+    </aside>
+  );
+}