feat: add git-consistent memory gateway architecture

gateway/tests/test_health.py

@@ -0,0 +1,9 @@
+from __future__ import annotations
+
+
+def test_health(client):
+    resp = client.get("/health")
+    assert resp.status_code == 200
+    payload = resp.json()
+    assert payload["ok"] is True
+    assert payload["service"] == "memory-gateway"