Limits are now account-tied rather than task-tied

include/Models.h

@@ -9,3 +9,8 @@ struct TaskRow {
     std::string status;  // serialized, see StatusUtil::serialize
     std::string notes;   // free text, any length (stored as SQLite TEXT)
 };
+
+struct AccountRow {
+    std::string id;
+    std::optional<std::string> cooldown;  // the account's wait: when its limit ends (StatusUtil::timeToText)
+};