chore(env): add bundled test accounts and seed admin

frontend/src/app/auth/page.tsx

@@ -13,8 +13,12 @@ export default function AuthPage() {
   );
 
   const [mode, setMode] = useState<"register" | "login">("register");
-  const [username, setUsername] = useState("");
-  const [password, setPassword] = useState("");
+  const [username, setUsername] = useState(
+    process.env.NEXT_PUBLIC_TEST_USERNAME ?? ""
+  );
+  const [password, setPassword] = useState(
+    process.env.NEXT_PUBLIC_TEST_PASSWORD ?? ""
+  );
   const [loading, setLoading] = useState(false);
   const [resp, setResp] = useState<AuthResp | null>(null);