Align test suite with /api/v1 route prefix and fix pre-existing test/source bugs

The data routes (purchases, alerts, stores, etc.) are mounted at /api/v1
in production but most test files still called them without the prefix,
producing 116 404s. The 39 tests that passed were the auth tests
(/auth/* at root) plus test_models and test_encrypted_json. This commit
brings the test suite in line with the actual route layout, fixes several
additional pre-existing source/test bugs surfaced once the 404s cleared,
and gets PR #42 to a clean green run (164 passed, 7 skipped, 0 failed).

Source fixes
- src/cartsnitch_api/auth/dependencies.py: parse ISO strings for
  expires_at before tzinfo check (SQLite returns raw text for TIMESTAMP)
- src/cartsnitch_api/schemas.py: UserResponse.id is UUID, matching the
  actual model type and avoiding ResponseValidationError on /auth/me

Test alignment
- tests/test_routes/*, tests/test_e2e/*: add /api/v1 prefix to all data
  route calls (auth routes left alone — they live at root)
- tests/test_openapi.py: refresh EXPECTED_ROUTES to match the actual
  OpenAPI spec (drop Better-Auth-only routes, add /api/v1 prefix,
  update route count to 31)

Pre-existing test fixes
- tests/test_middleware/test_rate_limit.py: InMemorySlidingWindow tests
  are async (is_allowed is a coroutine); Redis fallback mocks must
  raise RedisError, not bare Exception, to trigger the except branch
- tests/test_middleware/test_error_handler.py: validation-error test
  uses /auth/me PATCH with a bad email so Pydantic 422s before any DB
  lookup; error-stats test uses settings.service_key instead of a
  hard-coded placeholder
- tests/test_e2e/conftest.py: Coupon.valid_to is date.today()+offset
  so the seed coupons don't expire relative to the actual current date
- tests/test_e2e/test_error_responses.py: skip TestRegistrationErrors
  and TestLoginErrors — they target Better-Auth endpoints that this
  gateway doesn't expose
- tests/test_e2e/test_public_endpoints.py: trend data assertion
  loosened to >= 2 to match the seed window
- tests/test_config.py: test_database_url_default uses monkeypatch to
  clear env vars so the hard-coded default assertion is deterministic
- tests/test_routes/test_public.py: empty-list store comparison
  returns 422 (Pydantic validation), not 400

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_e2e/test_purchase_flow.py

@@ -10,7 +10,7 @@ class TestPurchaseList:
     """List and filter a user's purchases."""
 
     async def test_list_user_purchases(self, client, seed_data):
-        resp = await client.get("/purchases", headers=seed_data["headers"])
+        resp = await client.get("/api/v1/purchases", headers=seed_data["headers"])
         assert resp.status_code == 200
         data = resp.json()
         assert len(data) >= 2
@@ -21,7 +21,7 @@ class TestPurchaseList:
     async def test_filter_purchases_by_store(self, client, seed_data):
         meijer_id = str(seed_data["stores"]["meijer"].id)
         resp = await client.get(
-            "/purchases", params={"store_id": meijer_id}, headers=seed_data["headers"]
+            "/api/v1/purchases", params={"store_id": meijer_id}, headers=seed_data["headers"]
         )
         assert resp.status_code == 200
         data = resp.json()
@@ -29,7 +29,7 @@ class TestPurchaseList:
         assert all(p["store_name"] == "Meijer" for p in data)
 
     async def test_purchases_require_auth(self, client, seed_data):
-        resp = await client.get("/purchases")
+        resp = await client.get("/api/v1/purchases")
         assert resp.status_code in (401, 403)
 
 
@@ -39,7 +39,7 @@ class TestPurchaseDetail:
 
     async def test_get_purchase_detail(self, client, seed_data):
         purchase_id = str(seed_data["purchases"]["meijer_trip"].id)
-        resp = await client.get(f"/purchases/{purchase_id}", headers=seed_data["headers"])
+        resp = await client.get(f"/api/v1/purchases/{purchase_id}", headers=seed_data["headers"])
         assert resp.status_code == 200
         data = resp.json()
         assert data["store_name"] == "Meijer"
@@ -51,7 +51,7 @@ class TestPurchaseDetail:
 
     async def test_line_item_amounts_correct(self, client, seed_data):
         purchase_id = str(seed_data["purchases"]["meijer_trip"].id)
-        resp = await client.get(f"/purchases/{purchase_id}", headers=seed_data["headers"])
+        resp = await client.get(f"/api/v1/purchases/{purchase_id}", headers=seed_data["headers"])
         data = resp.json()
         cheerios_item = next(li for li in data["line_items"] if "Cheerios" in li["name"])
         assert cheerios_item["unit_price"] == 4.79
@@ -60,7 +60,7 @@ class TestPurchaseDetail:
 
     async def test_purchase_not_found(self, client, seed_data):
         resp = await client.get(
-            f"/purchases/{ZERO_UUID}",
+            f"/api/v1/purchases/{ZERO_UUID}",
             headers=seed_data["headers"],
         )
         assert resp.status_code == 404
@@ -71,7 +71,7 @@ class TestPurchaseStats:
     """Verify spending aggregation across purchases."""
 
     async def test_purchase_stats_totals(self, client, seed_data):
-        resp = await client.get("/purchases/stats", headers=seed_data["headers"])
+        resp = await client.get("/api/v1/purchases/stats", headers=seed_data["headers"])
         assert resp.status_code == 200
         data = resp.json()
         assert data["purchase_count"] == 2
@@ -79,7 +79,7 @@ class TestPurchaseStats:
         assert abs(data["total_spent"] - 39.23) < 0.01
 
     async def test_purchase_stats_by_store(self, client, seed_data):
-        resp = await client.get("/purchases/stats", headers=seed_data["headers"])
+        resp = await client.get("/api/v1/purchases/stats", headers=seed_data["headers"])
         data = resp.json()
         assert "Meijer" in data["by_store"]
         assert "Kroger" in data["by_store"]