feat: centralize routes and navigation guards

tests/component/router.test.jsx

@@ -0,0 +1,24 @@
+// @vitest-environment jsdom
+
+import { render, screen } from "@testing-library/react";
+import { describe, expect, it } from "vitest";
+
+import { createAnonymousSessionAdapter } from "../../src/adapters/auth/external-session-adapter.js";
+import { AppRouter } from "../../src/presentation/routes/app-router.jsx";
+
+describe("application router", () => {
+  it("renders not-found without making an API request", () => {
+    window.history.pushState({}, "", "/missing");
+    render(<AppRouter authSession={createAnonymousSessionAdapter()} />);
+    expect(
+      screen.getByRole("heading", { name: "페이지를 찾을 수 없습니다." }),
+    ).toBeVisible();
+  });
+
+  it("shows session-required UX without claiming authorization", () => {
+    window.history.pushState({}, "", "/sample/resources");
+    render(<AppRouter authSession={createAnonymousSessionAdapter()} />);
+    expect(screen.getByRole("heading", { name: "세션이 필요합니다." })).toBeVisible();
+    expect(screen.getByRole("button", { name: "로그인" })).toBeVisible();
+  });
+});