The tracker query result is JSON with the following schema:

> File := {
    today  := Seconds;
    week   := Seconds;
    month  := Seconds;
    year   := Seconds;
    custom := {
      since: "" or Date,
      until: "" or Date,
      total: Seconds,
      tasks: { slot:string, total:Seconds }[],
    },
  }

  Date    := string in ISO form yyyy-mm-dd
  Seconds := number
