Add per-consumer accepted import tolerance for wallboxes

With a 4.6kW inverter and 4kW WallboxB + ~450W house load, any PV dip
causes brief grid import and would trigger shutdown/restart cycling.

New config: wallbox_a_accepted_import_w / wallbox_b_accepted_import_w
WallboxB set to 600W: engine skips shutdown if import <= 600W, keeping
the car charging through short cloud shadows. WallboxA disabled (2kW
leaves sufficient inverter headroom without needing tolerance).

Logic: shutdownLastConsumer checks per-consumer tolerance before
applying min-runtime and initiating turn-off.

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

internal/engine/engine.go

@@ -146,7 +146,7 @@ func (e *Engine) Decide(state collector.SystemState, now time.Time, wwBoostC flo
 		}
 		importDuration := now.Sub(e.hyst.ImportSinceAbove)
 		if importDuration >= e.cfg.Hysteresis.ImportOffDurationParsed() {
-			if a := e.shutdownLastConsumer(now); a != nil {
+			if a := e.shutdownLastConsumer(now, gridW); a != nil {
 				actions = append(actions, *a)
 				e.hyst.ImportSinceAbove = time.Time{}
 			}
@@ -352,7 +352,8 @@ func (e *Engine) evaluateTurnOn(
 
 // shutdownLastConsumer turns off the lowest-priority active consumer
 // that has exceeded its minimum runtime.
-func (e *Engine) shutdownLastConsumer(now time.Time) *Action {
+// gridW is the current grid power (positive = import) used to check per-consumer import tolerance.
+func (e *Engine) shutdownLastConsumer(now time.Time, gridW float64) *Action {
 	// Reverse priority: WallboxB → WallboxA → WW → SGReady
 	order := []Consumer{ConsumerWallboxB, ConsumerWallboxA, ConsumerWW, ConsumerSGReady}
 
@@ -371,6 +372,24 @@ func (e *Engine) shutdownLastConsumer(now time.Time) *Action {
 			continue
 		}
 
+		// Per-consumer accepted import tolerance: if the current import is within
+		// the configured tolerance for this wallbox, skip shutdown.
+		var acceptedImportW float64
+		switch c {
+		case ConsumerWallboxA:
+			acceptedImportW = e.cfg.Consumers.WallboxAAcceptedImportW
+		case ConsumerWallboxB:
+			acceptedImportW = e.cfg.Consumers.WallboxBAcceptedImportW
+		}
+		if acceptedImportW > 0 && gridW <= acceptedImportW {
+			e.logger.Debug("skipping shutdown, import within accepted tolerance",
+				"consumer", c,
+				"grid_w", gridW,
+				"accepted_import_w", acceptedImportW,
+			)
+			continue
+		}
+
 		minRuntime := e.minRuntime(c)
 		runtime := now.Sub(cs.ActivatedAt)
 		if runtime < minRuntime {