feat(limit): add opt-in daily download limit core, history store and enforcement

Records every successful audiobook download in the library database (a new
DownloadHistory table) and, when the user opts in, stops downloading once the
rolling 24 hour window is full.

The history lives in the database rather than a file under LibationFiles
because in Docker only the database is on a volume; a file there is discarded
on every container restart.

The limit is checked immediately before each book downloads, never at queueing
time, so a full queue stays full and the user can raise or disable the limit
mid-run. When nothing in the queue can proceed the queue pauses and re-checks
every 15 seconds, recomputing settings, history and clock from scratch, so a
queue left running for days drip-feeds itself as downloads age out. The CLI
never waits: it skips covered titles and reports a count.

Co-authored-by: rmcrackan <rmcrackan@gmail.com>

Source/LibationWinForms/ProcessQueue/ProcessQueueControl.cs

@@ -67,11 +67,7 @@ internal partial class ProcessQueueControl : UserControl
 	}
 
 	private async void cancelAllBtn_Click(object? sender, EventArgs e)
-	{
-		ViewModel.Queue.ClearQueue();
-		if (ViewModel.Queue.Current is not null)
-			await ViewModel.Queue.Current.CancelAsync();
-	}
+		=> await ViewModel.CancelAllAsync();
 
 	private void btnClearFinished_Click(object? sender, EventArgs e)
 	{