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_prices.py

@@ -0,0 +1,90 @@
+"""Integration tests for price endpoints."""
+
+from datetime import date
+from decimal import Decimal
+
+import pytest
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker
+
+from cartsnitch_api.models import NormalizedProduct, PriceHistory, Store
+
+
+@pytest.fixture
+async def price_data(db_engine, auth_headers):
+    """Seed products with price history showing an increase."""
+    factory = async_sessionmaker(db_engine, class_=AsyncSession, expire_on_commit=False)
+    async with factory() as session:
+        store = Store(name="Walmart", slug="walmart")
+        product = NormalizedProduct(
+            canonical_name="Tide Pods 42ct",
+            category="household",
+            brand="Tide",
+        )
+        session.add_all([store, product])
+        await session.commit()
+        await session.refresh(store)
+        await session.refresh(product)
+
+        # Two price points — second is higher (increase)
+        ph1 = PriceHistory(
+            normalized_product_id=product.id,
+            store_id=store.id,
+            observed_date=date(2026, 2, 1),
+            regular_price=Decimal("12.99"),
+            source="receipt",
+        )
+        ph2 = PriceHistory(
+            normalized_product_id=product.id,
+            store_id=store.id,
+            observed_date=date(2026, 3, 1),
+            regular_price=Decimal("14.49"),
+            source="receipt",
+        )
+        session.add_all([ph1, ph2])
+        await session.commit()
+
+        return {"product": product, "store": store, "headers": auth_headers}
+
+
+@pytest.mark.asyncio
+async def test_price_trends(client, price_data):
+    resp = await client.get("/prices/trends", headers=price_data["headers"])
+    assert resp.status_code == 200
+    data = resp.json()
+    assert len(data) >= 1
+    assert data[0]["product_name"] == "Tide Pods 42ct"
+    assert len(data[0]["data_points"]) == 2
+
+
+@pytest.mark.asyncio
+async def test_price_trends_by_category(client, price_data):
+    resp = await client.get("/prices/trends?category=household", headers=price_data["headers"])
+    assert resp.status_code == 200
+    assert len(resp.json()) == 1
+
+    resp = await client.get("/prices/trends?category=nonexistent", headers=price_data["headers"])
+    assert resp.status_code == 200
+    assert len(resp.json()) == 0
+
+
+@pytest.mark.asyncio
+async def test_price_increases(client, price_data):
+    resp = await client.get("/prices/increases", headers=price_data["headers"])
+    assert resp.status_code == 200
+    data = resp.json()
+    assert len(data) >= 1
+    increase = data[0]
+    assert increase["old_price"] == 12.99
+    assert increase["new_price"] == 14.49
+    assert increase["increase_pct"] > 0
+
+
+@pytest.mark.asyncio
+async def test_price_comparison(client, price_data):
+    pid = str(price_data["product"].id)
+    resp = await client.get(f"/prices/comparison?product_ids={pid}", headers=price_data["headers"])
+    assert resp.status_code == 200
+    data = resp.json()
+    assert len(data) >= 1
+    assert data[0]["product_name"] == "Tide Pods 42ct"
+    assert len(data[0]["prices"]) >= 1