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_price_history.py

@@ -8,7 +8,7 @@ class TestPriceTrends:
     """Verify price trend aggregation against seeded history."""
 
     async def test_trends_returns_all_products(self, client, seed_data):
-        resp = await client.get("/prices/trends", headers=seed_data["headers"])
+        resp = await client.get("/api/v1/prices/trends", headers=seed_data["headers"])
         assert resp.status_code == 200
         data = resp.json()
         product_names = [t["product_name"] for t in data]
@@ -17,7 +17,7 @@ class TestPriceTrends:
 
     async def test_trends_filter_by_category(self, client, seed_data):
         resp = await client.get(
-            "/prices/trends", params={"category": "dairy"}, headers=seed_data["headers"]
+            "/api/v1/prices/trends", params={"category": "dairy"}, headers=seed_data["headers"]
         )
         assert resp.status_code == 200
         data = resp.json()
@@ -27,7 +27,7 @@ class TestPriceTrends:
             assert trend["product_name"] == "Whole Milk 1gal"
 
     async def test_trends_contain_data_points(self, client, seed_data):
-        resp = await client.get("/prices/trends", headers=seed_data["headers"])
+        resp = await client.get("/api/v1/prices/trends", headers=seed_data["headers"])
         data = resp.json()
         cheerios_trend = next(t for t in data if t["product_name"] == "Cheerios 18oz")
         assert len(cheerios_trend["data_points"]) >= 3
@@ -38,7 +38,7 @@ class TestPriceIncreases:
     """Detect price increases from seeded price history."""
 
     async def test_increases_detected(self, client, seed_data):
-        resp = await client.get("/prices/increases", headers=seed_data["headers"])
+        resp = await client.get("/api/v1/prices/increases", headers=seed_data["headers"])
         assert resp.status_code == 200
         data = resp.json()
         # Cheerios at Meijer went from 3.99 → 4.29 → 4.79
@@ -52,7 +52,7 @@ class TestPriceIncreases:
 
     async def test_stable_prices_not_flagged(self, client, seed_data):
         """Kroger Cheerios price is stable at $4.49 — should not appear as increase."""
-        resp = await client.get("/prices/increases", headers=seed_data["headers"])
+        resp = await client.get("/api/v1/prices/increases", headers=seed_data["headers"])
         data = resp.json()
         kroger_increases = [
             inc
@@ -69,7 +69,7 @@ class TestPriceComparison:
     async def test_compare_cheerios_across_stores(self, client, seed_data):
         cheerios_id = str(seed_data["products"]["cheerios"].id)
         resp = await client.get(
-            "/prices/comparison",
+            "/api/v1/prices/comparison",
             params={"product_ids": cheerios_id},
             headers=seed_data["headers"],
         )
@@ -84,14 +84,14 @@ class TestPriceComparison:
 
     async def test_compare_requires_product_ids(self, client, seed_data):
         """product_ids is required — omitting it must return 422."""
-        resp = await client.get("/prices/comparison", headers=seed_data["headers"])
+        resp = await client.get("/api/v1/prices/comparison", headers=seed_data["headers"])
         assert resp.status_code == 422
 
     async def test_compare_multiple_products(self, client, seed_data):
         cheerios_id = str(seed_data["products"]["cheerios"].id)
         milk_id = str(seed_data["products"]["milk"].id)
         resp = await client.get(
-            "/prices/comparison",
+            "/api/v1/prices/comparison",
             params=[("product_ids", cheerios_id), ("product_ids", milk_id)],
             headers=seed_data["headers"],
         )