Add export plan guard to block Deye export against plan.

Force PASSIVE/no-export when sell is negative or export_mode is NONE,
and alert NEG_SELL_EXPORT in plan_actual_slot_guard when export still occurs.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/services/control/exporter_monolith.py

@@ -59,6 +59,7 @@ from services.control.repository import (
 )
 from services.control.setpoints import (
     _DictRecord,
+    _apply_export_plan_guard,
     _apply_price_failsafe_guard,
     _build_setpoints,
     _clamp_deye_tou_soc_pct,