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_purchases.py

@@ -0,0 +1,95 @@
+"""Integration tests for purchase endpoints."""
+
+import uuid
+from datetime import date
+from decimal import Decimal
+
+import pytest
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker
+
+from cartsnitch_api.auth.jwt import create_access_token
+from cartsnitch_api.models import Purchase, PurchaseItem, Store, User
+
+
+@pytest.fixture
+async def purchase_data(db_engine):
+    """Seed a user, store, purchase, and items."""
+    factory = async_sessionmaker(db_engine, class_=AsyncSession, expire_on_commit=False)
+    async with factory() as session:
+        from cartsnitch_api.auth.passwords import hash_password
+
+        user = User(
+            email="buyer@example.com",
+            hashed_password=hash_password("testpass123"),
+            display_name="Buyer",
+        )
+        store = Store(name="Kroger", slug="kroger")
+        session.add_all([user, store])
+        await session.commit()
+        await session.refresh(user)
+        await session.refresh(store)
+
+        purchase = Purchase(
+            user_id=user.id,
+            store_id=store.id,
+            receipt_id="receipt-001",
+            purchase_date=date(2026, 3, 10),
+            total=Decimal("42.50"),
+        )
+        session.add(purchase)
+        await session.commit()
+        await session.refresh(purchase)
+
+        item = PurchaseItem(
+            purchase_id=purchase.id,
+            product_name_raw="Organic Milk 1gal",
+            quantity=Decimal("1"),
+            unit_price=Decimal("5.99"),
+            extended_price=Decimal("5.99"),
+        )
+        session.add(item)
+        await session.commit()
+
+        token = create_access_token(user.id)
+        return {
+            "user": user,
+            "store": store,
+            "purchase": purchase,
+            "headers": {"Authorization": f"Bearer {token}"},
+        }
+
+
+@pytest.mark.asyncio
+async def test_list_purchases(client, purchase_data):
+    resp = await client.get("/purchases", headers=purchase_data["headers"])
+    assert resp.status_code == 200
+    data = resp.json()
+    assert len(data) == 1
+    assert data[0]["store_name"] == "Kroger"
+    assert data[0]["total"] == 42.50
+
+
+@pytest.mark.asyncio
+async def test_get_purchase_detail(client, purchase_data):
+    pid = str(purchase_data["purchase"].id)
+    resp = await client.get(f"/purchases/{pid}", headers=purchase_data["headers"])
+    assert resp.status_code == 200
+    data = resp.json()
+    assert len(data["line_items"]) == 1
+    assert data["line_items"][0]["name"] == "Organic Milk 1gal"
+
+
+@pytest.mark.asyncio
+async def test_get_purchase_not_found(client, auth_headers):
+    resp = await client.get(f"/purchases/{uuid.uuid4()}", headers=auth_headers)
+    assert resp.status_code == 404
+
+
+@pytest.mark.asyncio
+async def test_purchase_stats(client, purchase_data):
+    resp = await client.get("/purchases/stats", headers=purchase_data["headers"])
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["total_spent"] == 42.50
+    assert data["purchase_count"] == 1
+    assert "Kroger" in data["by_store"]