feat(client): add UI kit, data layer, app shell, and Table component

- design token system (Atlantis, Kimberly, Powder Ash palette)
- Button, Badge, Input, Select, Card, SidePanel, Breadcrumbs components
- generic typed Table<T> component with loading/empty states
- API data layer: typed fetch client for environments, keys, sessions, scenarios
- Vite dev proxy targeting server on port 13000
- App shell with SidePanel nav and four entity pages (Environments, Keys, Sessions, Scenarios)
- Storybook config with dark/light theme toggle and a11y addon

client/src/pages/KeysPage.tsx

@@ -0,0 +1,38 @@
+import { useEffect, useState } from 'react';
+import { keys } from '../api';
+import { Table, type TableColumn } from '../ui';
+import styles from './Page.module.css';
+
+interface KeyRow { name: string }
+
+const columns: TableColumn<KeyRow>[] = [
+  { key: 'name', header: 'Key name', render: (k) => k.name },
+];
+
+export function KeysPage() {
+  const [items, setItems] = useState<KeyRow[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+
+  useEffect(() => {
+    setLoading(true);
+    keys.list()
+      .then((res) => setItems(res.keys.map((name) => ({ name }))))
+      .catch((err: Error) => setError(err.message))
+      .finally(() => setLoading(false));
+  }, []);
+
+  return (
+    <div>
+      <h1 className={styles.heading}>Keys</h1>
+      {error && <p className={styles.error}>{error}</p>}
+      <Table
+        columns={columns}
+        data={items}
+        rowKey={(k) => k.name}
+        loading={loading}
+        emptyMessage="No key files found."
+      />
+    </div>
+  );
+}