Default online backtest to production GTL

tests/unit/test_backtest_service.py

@@ -793,6 +793,9 @@ def test_window_setups_too_short_returns_empty():
 
 
 def test_sr_research_variant_is_explicit_and_validated(monkeypatch):
+    monkeypatch.delenv("BACKTEST_SR_VARIANT", raising=False)
+    assert bt._sr_research_variant() == bt.EXPLICIT_TARGET_LADDER_VARIANT
+
     for variant in (
         "production_control",
         "legacy_range_grid_touch",