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_e2e/test_error_responses.py

@@ -0,0 +1,127 @@
+"""E2E: Error responses for bad input across all endpoint categories."""
+
+import pytest
+
+from tests.test_e2e.conftest import BAD_UUID, ZERO_UUID
+
+
+@pytest.mark.asyncio
+class TestRegistrationErrors:
+    """Validation errors during user registration."""
+
+    async def test_short_password(self, client, db_engine):
+        resp = await client.post(
+            "/auth/register",
+            json={"email": "short@example.com", "password": "short", "display_name": "Test"},
+        )
+        assert resp.status_code == 422
+
+    async def test_invalid_email(self, client, db_engine):
+        resp = await client.post(
+            "/auth/register",
+            json={"email": "not-an-email", "password": "securepass123", "display_name": "Test"},
+        )
+        assert resp.status_code == 422
+
+    async def test_missing_fields(self, client, db_engine):
+        resp = await client.post("/auth/register", json={})
+        assert resp.status_code == 422
+
+    async def test_empty_display_name(self, client, db_engine):
+        resp = await client.post(
+            "/auth/register",
+            json={"email": "empty@example.com", "password": "securepass123", "display_name": ""},
+        )
+        assert resp.status_code == 422
+
+    async def test_duplicate_email(self, client, db_engine):
+        payload = {
+            "email": "dupe@example.com",
+            "password": "securepass123",
+            "display_name": "First",
+        }
+        first = await client.post("/auth/register", json=payload)
+        assert first.status_code == 201
+        second = await client.post("/auth/register", json=payload)
+        assert second.status_code == 409
+
+
+@pytest.mark.asyncio
+class TestLoginErrors:
+    """Login failure modes."""
+
+    async def test_wrong_password(self, client, db_engine):
+        await client.post(
+            "/auth/register",
+            json={
+                "email": "login-err@example.com",
+                "password": "correctpass1",
+                "display_name": "Login",
+            },
+        )
+        resp = await client.post(
+            "/auth/login",
+            json={"email": "login-err@example.com", "password": "wrongpass123"},
+        )
+        assert resp.status_code == 401
+
+    async def test_nonexistent_user(self, client, db_engine):
+        resp = await client.post(
+            "/auth/login",
+            json={"email": "nobody@example.com", "password": "doesntmatter"},
+        )
+        assert resp.status_code == 401
+
+
+@pytest.mark.asyncio
+class TestNotFoundErrors:
+    """404 responses for missing resources."""
+
+    async def test_product_not_found(self, client, seed_data):
+        resp = await client.get(f"/products/{ZERO_UUID}", headers=seed_data["headers"])
+        assert resp.status_code == 404
+
+    async def test_purchase_not_found(self, client, seed_data):
+        resp = await client.get(f"/purchases/{ZERO_UUID}", headers=seed_data["headers"])
+        assert resp.status_code == 404
+
+    async def test_public_trend_not_found(self, client, seed_data):
+        resp = await client.get(f"/public/trends/{ZERO_UUID}")
+        assert resp.status_code == 404
+
+
+@pytest.mark.asyncio
+class TestMalformedInput:
+    """Invalid UUID formats and bad query params."""
+
+    async def test_invalid_uuid_product(self, client, seed_data):
+        resp = await client.get(f"/products/{BAD_UUID}", headers=seed_data["headers"])
+        assert resp.status_code == 422
+
+    async def test_invalid_uuid_purchase(self, client, seed_data):
+        resp = await client.get(f"/purchases/{BAD_UUID}", headers=seed_data["headers"])
+        assert resp.status_code == 422
+
+    async def test_invalid_uuid_public_trend(self, client, seed_data):
+        resp = await client.get(f"/public/trends/{BAD_UUID}")
+        assert resp.status_code == 422
+
+
+@pytest.mark.asyncio
+class TestStoreConnectionErrors:
+    """Store connection edge cases."""
+
+    async def test_connect_nonexistent_store(self, client, seed_data):
+        resp = await client.post(
+            "/me/stores/nonexistent-store/connect",
+            json={},
+            headers=seed_data["headers"],
+        )
+        assert resp.status_code == 404
+
+    async def test_connect_store_twice(self, client, seed_data):
+        headers = seed_data["headers"]
+        first = await client.post("/me/stores/meijer/connect", json={}, headers=headers)
+        assert first.status_code in (200, 201)
+        second = await client.post("/me/stores/meijer/connect", json={}, headers=headers)
+        assert second.status_code == 409