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_middleware/test_error_handler.py

@@ -2,6 +2,8 @@
 
 import pytest
 
+from cartsnitch_api.config import settings
+
 
 @pytest.mark.asyncio
 async def test_404_returns_structured_error(client):
@@ -15,11 +17,14 @@ async def test_404_returns_structured_error(client):
 
 
 @pytest.mark.asyncio
-async def test_validation_error_returns_422_with_field_errors(client):
+async def test_validation_error_returns_422_with_field_errors(client, auth_headers):
     """Invalid request body should return structured validation errors."""
-    resp = await client.post(
-        "/auth/register",
-        json={"email": "not-an-email", "password": "short", "display_name": ""},
+    # Use the auth/me PATCH endpoint with an invalid email — Pydantic will
+    # return 422 with structured field errors before any DB lookup runs.
+    resp = await client.patch(
+        "/auth/me",
+        json={"email": "not-an-email"},
+        headers=auth_headers,
     )
     assert resp.status_code == 422
     body = resp.json()
@@ -46,7 +51,7 @@ async def test_error_stats_with_valid_key(client):
     """Error stats endpoint returns monitoring data with valid key."""
     resp = await client.get(
         "/internal/error-stats",
-        headers={"X-Service-Key": "change-me-in-production"},
+        headers={"X-Service-Key": settings.service_key},
     )
     assert resp.status_code == 200
     body = resp.json()