Add configurable override duration and hard-stop thresholds

Override duration (web UI):
- Dropdown on Ein button: 30min / 1h / 2h / 4h
- Engine notified immediately via ApplyOverride() — no waiting for
  next SyncHardwareState cycle
- Aus button always uses 1h lockout (keeps consumer off for 1h)

Hard-stop thresholds that cancel active overrides:
- SOC emergency brake: now also clears ManualOverride flag so EMS
  resumes full control after the safety shutdown
- override_max_import_w (default 800W): if grid import exceeds this
  while an override is active, override is cancelled immediately
  (no hysteresis delay — protection is instant)

Config: ems.override_max_import_w (0 = disabled)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/engine/engine.go

@@ -123,6 +123,9 @@ func (e *Engine) Decide(state collector.SystemState, now time.Time, wwBoostC flo
 	// --- SOC emergency brake ---
 	actions = append(actions, e.socEmergencyBrake(soc, now)...)
 
+	// --- Override hard stop: cancel override on excessive import ---
+	actions = append(actions, e.overrideHardStop(gridW)...)
+
 	// --- WW window shutdown ---
 	// If WW is active but we're outside the allowed time window, reset immediately.
 	if cs := e.consumers[ConsumerWW]; cs.Active && !wwWindow {
@@ -400,7 +403,7 @@ func (e *Engine) shutdownLastConsumer(now time.Time) *Action {
 }
 
 // socEmergencyBrake immediately shuts off consumers whose SOC threshold
-// is no longer met, ignoring minimum runtimes.
+// is no longer met, ignoring minimum runtimes and manual overrides.
 func (e *Engine) socEmergencyBrake(soc float64, now time.Time) []Action {
 	var actions []Action
 	allowed := e.allowedConsumers(soc)
@@ -416,9 +419,12 @@ func (e *Engine) socEmergencyBrake(soc float64, now time.Time) []Action {
 		e.logger.Warn("SOC emergency brake",
 			"consumer", c,
 			"soc", soc,
+			"was_override", cs.ManualOverride,
 		)
 
 		cs.Active = false
+		cs.ManualOverride = false // EMS takes back full control after emergency
+		cs.OverrideUntil = time.Time{}
 		a := Action{
 			Consumer: c,
 			TurnOn:   false,
@@ -433,6 +439,69 @@ func (e *Engine) socEmergencyBrake(soc float64, now time.Time) []Action {
 	return actions
 }
 
+// overrideHardStop cancels active overrides when grid import exceeds the
+// configured hard-stop threshold. Called before normal shutdown logic so
+// there is no hysteresis delay — protection is immediate.
+func (e *Engine) overrideHardStop(gridW float64) []Action {
+	limit := e.cfg.EMS.OverrideMaxImportW
+	if limit <= 0 || gridW <= limit {
+		return nil
+	}
+
+	var actions []Action
+	for c, cs := range e.consumers {
+		if !cs.Active || !cs.ManualOverride {
+			continue
+		}
+
+		e.logger.Warn("override hard stop: import exceeds limit",
+			"consumer", c,
+			"grid_w", gridW,
+			"limit_w", limit,
+		)
+
+		cs.Active = false
+		cs.ManualOverride = false
+		cs.OverrideUntil = time.Time{}
+		a := Action{
+			Consumer: c,
+			TurnOn:   false,
+			Reason:   fmt.Sprintf("override cancelled: import %.0fW > limit %.0fW", gridW, limit),
+		}
+		if c == ConsumerWW {
+			a.TargetTempC = e.cfg.Strategic.WWBaseC
+		}
+		actions = append(actions, a)
+	}
+	return actions
+}
+
+// ApplyOverride directly sets a consumer's state and override lockout.
+// Called from the web UI override handler so the engine state is consistent
+// immediately, without waiting for the next SyncHardwareState cycle.
+func (e *Engine) ApplyOverride(consumer Consumer, on bool, duration time.Duration) {
+	cs, ok := e.consumers[consumer]
+	if !ok {
+		return
+	}
+	now := time.Now()
+	cs.Active = on
+	cs.ManualOverride = true
+	cs.OverrideUntil = now.Add(duration)
+	cs.LowPowerCycles = 0
+	if on {
+		cs.ActivatedAt = now
+	} else {
+		cs.ActivatedAt = time.Time{}
+	}
+	e.logger.Info("manual override applied",
+		"consumer", consumer,
+		"on", on,
+		"duration", duration,
+		"until", cs.OverrideUntil.Format("15:04"),
+	)
+}
+
 // isHeatingPeriod returns true if the current month is within the heating season.
 func (e *Engine) isHeatingPeriod(now time.Time) bool {
 	month := int(now.Month())