fix: use SQLite-compatible space format in utcnow_iso(), fix credits ordering

utcnow_iso() now produces 'YYYY-MM-DD HH:MM:SS' (space separator) matching
SQLite's datetime('now') so lexicographic comparisons like
'published_at <= datetime(now)' work correctly.

Also add `id DESC` tiebreaker to get_ledger() ORDER BY to preserve
insertion order when multiple credits are added within the same second.

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

web/tests/test_seo.py

@@ -1,11 +1,10 @@
 """Tests for the SEO metrics module: queries, sync functions, admin routes."""
 
 from datetime import UTC, datetime, timedelta
-
-from padelnomics.core import utcnow_iso
 from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
+from padelnomics.core import utcnow_iso
 from padelnomics.seo._queries import (
     cleanup_old_metrics,
     get_article_scorecard,