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/admin/test_secrets_router.py

@@ -0,0 +1,35 @@
+from __future__ import annotations
+
+
+def _login(client, email: str, password: str) -> dict[str, str]:
+    response = client.post("/api/v1/auth/login", json={"email": email, "password": password})
+    assert response.status_code == 200
+    return {"Authorization": f"Bearer {response.json()['access_token']}"}
+
+
+def test_superuser_can_read_install_secrets(client):
+    headers = _login(client, "admin@compton.example", "Admin1234")
+    response = client.get("/api/v1/admin/secrets", headers=headers)
+    assert response.status_code == 200
+    payload = response.json()
+    assert "secrets_status" in payload
+    assert payload["secrets_status"]["postgres_password"] in {"configured", "missing"}
+    assert "POSTGRES_PASSWORD" not in str(payload)
+
+
+def test_non_superuser_cannot_read_install_secrets(client):
+    headers = _login(client, "ops@compton.example", "OpsAdmin1234")
+    response = client.get("/api/v1/admin/secrets", headers=headers)
+    assert response.status_code == 403
+
+
+def test_superuser_can_reveal_db_password(client):
+    headers = _login(client, "admin@compton.example", "Admin1234")
+    response = client.post(
+        "/api/v1/admin/secrets/reveal",
+        headers=headers,
+        json={"key": "database_password"},
+    )
+    assert response.status_code == 200
+    assert response.json()["key"] == "database_password"
+    assert "value" in response.json()