feat(gateway): automation rule engine and reminder scheduler

- engine: 5-field cron parser (*/n, ranges, lists) firing at most once
  per minute; device-state triggers with edge detection; manual trigger
  via POST /automation/rules/:id/trigger; actions run through the AI
  pipeline so rules can call any tool (IoT control, search, ...)
- reminders: due-scan scheduler delivering via WebSocket broadcast,
  optional LLM-polished reminder text with plain-title fallback;
  Reminder gains Done flag with ListDue/MarkDone
- tests: cron matching and validation, once-per-minute dedup, device
  edge triggering, manual trigger, reminder delivery

backend/services/gateway/api/router.go

@@ -86,6 +86,11 @@ type BridgeConfigManager interface {
 	DeleteAdapter(name string) error
 }
 
+// AutomationEngine fires automation rules immediately.
+type AutomationEngine interface {
+	Trigger(ctx context.Context, id string) error
+}
+
 // ChatStorer persists chat sessions and messages.
 type ChatStorer interface {
 	CreateSession(ctx context.Context, id, userID, title string) (*store.Session, error)
@@ -110,6 +115,7 @@ type Dependencies struct {
 	ChatStore    ChatStorer
 	ModelConfig  *ModelConfigStore
 	Automation   *AutomationStore
+	AutomationEng AutomationEngine
 	Reminders    *ReminderStore
 	PluginList   []map[string]string
 }