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/api/tests/modules/users/test_users_router.py

@@ -0,0 +1,30 @@
+from tests.helpers import register_verify_login
+
+
+def test_me_endpoint(client):
+    headers = register_verify_login(client, "me@example.com", "Valid123")
+    response = client.get("/api/v1/users/me", headers=headers)
+    assert response.status_code == 200
+    assert response.json()["user"]["email"] == "me@example.com"
+
+
+def test_patch_me_updates_display_name(client):
+    headers = register_verify_login(client, "display@example.com", "Valid123")
+    response = client.patch(
+        "/api/v1/users/me",
+        headers=headers,
+        json={"display_name": "Updated Name"},
+    )
+    assert response.status_code == 200
+    assert response.json()["profile"]["display_name"] == "Updated Name"
+
+
+def test_change_password_rejects_invalid_current(client):
+    headers = register_verify_login(client, "pwd@example.com", "Valid123")
+    response = client.post(
+        "/api/v1/users/me/password",
+        headers=headers,
+        json={"current_password": "Wrong123", "new_password": "NewValid1"},
+    )
+    assert response.status_code == 400
+    assert response.json()["detail"] == "INVALID_CURRENT_PASSWORD"