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_public.py

@@ -0,0 +1,73 @@
+"""Integration tests for public endpoints (no auth)."""
+
+import uuid
+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 public_data(db_engine):
+    """Seed data for public endpoints."""
+    factory = async_sessionmaker(db_engine, class_=AsyncSession, expire_on_commit=False)
+    async with factory() as session:
+        store = Store(name="Target", slug="target")
+        product = NormalizedProduct(
+            canonical_name="Skippy PB 16oz",
+            category="pantry",
+            brand="Skippy",
+        )
+        session.add_all([store, product])
+        await session.commit()
+        await session.refresh(store)
+        await session.refresh(product)
+
+        ph = PriceHistory(
+            normalized_product_id=product.id,
+            store_id=store.id,
+            observed_date=date(2026, 3, 5),
+            regular_price=Decimal("3.99"),
+            source="receipt",
+        )
+        session.add(ph)
+        await session.commit()
+
+        return {"product": product, "store": store}
+
+
+@pytest.mark.asyncio
+async def test_public_trend(client, public_data):
+    pid = str(public_data["product"].id)
+    resp = await client.get(f"/public/trends/{pid}")
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["product_name"] == "Skippy PB 16oz"
+    assert len(data["data_points"]) == 1
+
+
+@pytest.mark.asyncio
+async def test_public_trend_not_found(client):
+    resp = await client.get(f"/public/trends/{uuid.uuid4()}")
+    assert resp.status_code == 404
+
+
+@pytest.mark.asyncio
+async def test_public_store_comparison(client, public_data):
+    pid = str(public_data["product"].id)
+    resp = await client.get(f"/public/store-comparison?product_ids={pid}")
+    assert resp.status_code == 200
+    data = resp.json()
+    assert len(data["products"]) == 1
+
+
+@pytest.mark.asyncio
+async def test_public_inflation(client, public_data):
+    resp = await client.get("/public/inflation")
+    assert resp.status_code == 200
+    data = resp.json()
+    assert "categories" in data
+    assert "cartsnitch_index" in data