fix(tui,status,store): add delete confirm, input validation, XSS fix, history persistence

Prevent accidental deletes with y/n confirmation dialog. Validate all
numeric form inputs (interval, port, timeout, threshold, retries) with
range checks instead of silently defaulting to zero. Escape user-supplied
data in status page JavaScript to close XSS via monitor names. Persist
check history to new check_history table so sparklines and uptime
percentages survive restarts.

cmd/goupkeep/main.go

@@ -112,6 +112,7 @@ func main() {
 		fmt.Printf("Imported %d monitors and %d alerts from Uptime Kuma v%s\n", len(backup.Sites), len(backup.Alerts), kb.Version)
 	}
 
+	monitor.InitHistoryFromStore()
 	monitor.StartEngine()
 
 	server.Start(server.ServerConfig{