Add TOU SOC handling for battery priority in passive mode

- Introduced `effective_sell_price_czk_kwh` to `ControlSetpoints` for managing battery usage based on sell price.
- Implemented logic in `_deye_passive_tou_battery_soc_pct` to set TOU SOC to 100% when conditions favor battery usage.
- Updated tests to validate new behavior for negative sell prices and planned charging scenarios.
- Enhanced documentation to clarify TOU SOC behavior in passive mode.

backend/tests/test_control_exporter_tou.py

@@ -62,12 +62,50 @@ class DeyeTouParamsTests(unittest.TestCase):
             ev1_power_w=0,
             ev2_power_w=0,
             target_soc_pct=None,
+            effective_sell_price_czk_kwh=None,
         )
         self.assertEqual(get_deye_mode(sp), "PASSIVE")
         p, s, g = _deye_tou_params(sp, _inv(min_soc=12, reserve_soc=20))
         self.assertFalse(g)
         self.assertEqual(s, 12)
 
+    def test_passive_negative_sell_steers_tou_above_current_soc(self) -> None:
+        """Záporná vykupní → TOU SOC = 100 % (priorita akumulace vs. přetok)."""
+        sp = ControlSetpoints(
+            battery_w=-400,
+            grid_export_limit=0,
+            ev1_current_a=0,
+            ev2_current_a=0,
+            heat_pump_enable=False,
+            grid_setpoint_w=0,
+            ev1_power_w=0,
+            ev2_power_w=0,
+            target_soc_pct=14,
+            effective_sell_price_czk_kwh=-0.25,
+        )
+        self.assertEqual(get_deye_mode(sp), "PASSIVE")
+        _p, s, g = _deye_tou_params(sp, _inv(min_soc=12, reserve_soc=20))
+        self.assertFalse(g)
+        self.assertEqual(s, 100)
+
+    def test_passive_planned_charge_steers_tou(self) -> None:
+        sp = ControlSetpoints(
+            battery_w=800,
+            grid_export_limit=0,
+            ev1_current_a=0,
+            ev2_current_a=0,
+            heat_pump_enable=False,
+            grid_setpoint_w=0,
+            ev1_power_w=0,
+            ev2_power_w=0,
+            target_soc_pct=60,
+            effective_sell_price_czk_kwh=1.0,
+        )
+        self.assertEqual(get_deye_mode(sp), "PASSIVE")
+        _p, s, g = _deye_tou_params(sp, _inv(min_soc=12, reserve_soc=20))
+        self.assertFalse(g)
+        self.assertEqual(s, 100)
+
     def test_charge_unchanged_grid_charge(self) -> None:
         sp = ControlSetpoints(
             battery_w=5000,