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_feature_flags.py

@@ -7,16 +7,13 @@ Integration tests exercise full request/response flows via Quart test client.
 """
 
 import sqlite3
-
-from padelnomics.core import utcnow_iso
-from pathlib import Path
 from unittest.mock import AsyncMock, patch
 
 import pytest
-
-from padelnomics import core
+from padelnomics.core import utcnow_iso
 from padelnomics.migrations.migrate import migrate
 
+from padelnomics import core
 
 # ── Fixtures & helpers ────────────────────────────────────────────
 
@@ -294,8 +291,9 @@ class TestLeadUnlockGate:
     @pytest.mark.asyncio
     async def test_route_imports_is_flag_enabled(self):
         """suppliers/routes.py imports is_flag_enabled (gate is wired up)."""
-        from padelnomics.suppliers.routes import unlock_lead
         import inspect
+
+        from padelnomics.suppliers.routes import unlock_lead
         src = inspect.getsource(unlock_lead)
         assert "is_flag_enabled" in src
         assert "lead_unlock" in src