feat(tui): dismiss a finished download with d

A completed row used to ignore d: only a queued transfer could be pulled
out of the list, so a finished one sat there until the next restart. d
now goes through one handler that drops a finished row whatever the
session thinks of it — a completed transfer can live only in this window,
restored from an earlier run, where there is nothing to forget.

The finished-status test was spelled out twice in clear_finished_downloads
and had to agree by hand; both callers now share is_finished().

soulseek-rs/src/ui/main_tui/input.rs

@@ -428,7 +428,7 @@ impl MainTui {
                 self.toggle_selected_download_pause();
             }
             KeyCode::Char('d') => {
-                self.remove_selected_queued_download();
+                self.remove_selected_download();
             }
             KeyCode::Char('r') => {
                 self.retry_selected_download();