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_supervisor.py

@@ -8,19 +8,16 @@ supervisor.py lives in src/padelnomics/ (not a uv workspace package), so we
 add src/ to sys.path before importing.
 """
 
-import sys
+# Load supervisor.py directly by path — avoids clashing with the web app's
+# 'padelnomics' namespace (which is the installed web package).
+import importlib.util as _ilu
 import textwrap
-import tomllib
 from datetime import UTC, datetime, timedelta
 from pathlib import Path
 from unittest.mock import MagicMock, patch
 
 import pytest
 
-# Load supervisor.py directly by path — avoids clashing with the web app's
-# 'padelnomics' namespace (which is the installed web package).
-import importlib.util as _ilu
-
 _SUP_PATH = Path(__file__).parent.parent.parent / "src" / "padelnomics" / "supervisor.py"
 _spec = _ilu.spec_from_file_location("padelnomics_supervisor", _SUP_PATH)
 sup = _ilu.module_from_spec(_spec)
@@ -32,7 +29,6 @@ from padelnomics_extract.proxy import (
     make_sticky_selector,
 )
 
-
 # ── load_workflows ────────────────────────────────────────────────