fix(tests): replace datetime.utcnow() with utcnow_iso() in test files

Also fixes test_supplier_webhooks.py fromisoformat() comparisons:
expires (naive, from DB) now compared against datetime.now(UTC).replace(tzinfo=None)
to avoid mixing naive/aware datetimes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/tests/test_seo.py

@@ -1,6 +1,8 @@
 """Tests for the SEO metrics module: queries, sync functions, admin routes."""
 
-from datetime import datetime, timedelta
+from datetime import UTC, datetime, timedelta
+
+from padelnomics.core import utcnow_iso
 from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
@@ -21,11 +23,11 @@ from padelnomics import core
 # ── Fixtures ──────────────────────────────────────────────────
 
 def _today():
-    return datetime.utcnow().strftime("%Y-%m-%d")
+    return datetime.now(UTC).strftime("%Y-%m-%d")
 
 
 def _days_ago(n: int) -> str:
-    return (datetime.utcnow() - timedelta(days=n)).strftime("%Y-%m-%d")
+    return (datetime.now(UTC) - timedelta(days=n)).strftime("%Y-%m-%d")
 
 
 @pytest.fixture
@@ -72,7 +74,7 @@ async def seo_data(db):
 @pytest.fixture
 async def articles_data(db, seo_data):
     """Create articles that match the SEO data URLs."""
-    now = datetime.utcnow().isoformat()
+    now = utcnow_iso()
     pub = _days_ago(10)
 
     for title, url, tpl, lang in [
@@ -91,7 +93,7 @@ async def articles_data(db, seo_data):
 @pytest.fixture
 async def admin_client(app, db):
     """Authenticated admin client."""
-    now = datetime.utcnow().isoformat()
+    now = utcnow_iso()
     async with db.execute(
         "INSERT INTO users (email, name, created_at) VALUES (?, ?, ?)",
         ("admin@test.com", "Admin", now),
@@ -258,7 +260,7 @@ class TestSyncStatus:
     """Tests for get_sync_status()."""
 
     async def test_returns_last_sync_per_source(self, db):
-        now = datetime.utcnow().isoformat()
+        now = utcnow_iso()
         await db.execute(
             """INSERT INTO seo_sync_log (source, status, rows_synced, started_at, completed_at, duration_ms)
                VALUES ('gsc', 'success', 100, ?, ?, 500)""",
@@ -286,7 +288,7 @@ class TestCleanupOldMetrics:
     """Tests for cleanup_old_metrics()."""
 
     async def test_deletes_old_data(self, db):
-        old_date = (datetime.utcnow() - timedelta(days=400)).strftime("%Y-%m-%d")
+        old_date = (datetime.now(UTC) - timedelta(days=400)).strftime("%Y-%m-%d")
         recent_date = _today()
 
         await db.execute(