Update admin theme/layout and refresh README details.

Align the project baseline with the latest admin interface styling and layout structure while documenting setup and usage updates in README.

apps/web/src/shared/api/client.test.ts

@@ -0,0 +1,16 @@
+import { describe, expect, it } from "vitest";
+import { applyAuthHeader, setAccessTokenGetter } from "./client";
+
+describe("apiClient auth header", () => {
+  it("attaches bearer token from getter", () => {
+    setAccessTokenGetter(() => "test-token");
+    const headers = applyAuthHeader({});
+    expect(headers.Authorization).toBe("Bearer test-token");
+  });
+
+  it("leaves headers unchanged without token", () => {
+    setAccessTokenGetter(() => null);
+    const headers = applyAuthHeader({ "X-Test": "1" });
+    expect(headers).toEqual({ "X-Test": "1" });
+  });
+});