fix TypeScript types for AutoDismissFlash hook

assets/js/app.ts

@@ -371,15 +371,17 @@ const ScrollToTop = {
 
 // LiveView hook for auto-dismissing flash messages
 const AutoDismissFlash = {
-  mounted() {
+  timeout: null as ReturnType<typeof setTimeout> | null,
+  mounted(this: any) {
     const dismissAfter = parseInt(this.el.dataset.dismissAfter || "30000", 10)
     this.timeout = setTimeout(() => {
       this.el.click()
     }, dismissAfter)
   },
-  destroyed() {
+  destroyed(this: any) {
     if (this.timeout) {
       clearTimeout(this.timeout)
+      this.timeout = null
     }
   }
 }