feat: merge cartsnitch/api into api/ subdirectory

Consolidate API gateway service into monorepo.
Squashed from https://github.com/cartsnitch/api main (89bacb1).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

tests/test_routes/test_alerts.py

@@ -0,0 +1,35 @@
+"""Integration tests for alert endpoints."""
+
+import pytest
+
+
+@pytest.mark.asyncio
+async def test_list_alerts_empty(client, auth_headers):
+    """No purchases means no alerts."""
+    resp = await client.get("/alerts", headers=auth_headers)
+    assert resp.status_code == 200
+    assert resp.json() == []
+
+
+@pytest.mark.asyncio
+async def test_get_alert_settings(client, auth_headers):
+    resp = await client.get("/alerts/settings", headers=auth_headers)
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["price_increase_threshold_pct"] == 5.0
+    assert data["shrinkflation_enabled"] is True
+    assert data["email_notifications"] is False
+
+
+@pytest.mark.asyncio
+async def test_update_alert_settings_returns_501(client, auth_headers):
+    resp = await client.put(
+        "/alerts/settings",
+        headers=auth_headers,
+        json={
+            "price_increase_threshold_pct": 10.0,
+            "shrinkflation_enabled": False,
+            "email_notifications": True,
+        },
+    )
+    assert resp.status_code == 501