fix(stats): address CodeRabbit review on PR #50

- Guard episode deletion against double-submit with an isDeletingRef +
  setIsDeleting pair threaded through buildDeleteEpisodeHandler, and
  disable the MediaHeader delete button while a request is in flight.
- Restore MediaHeader title truncation by adding min-w-0 flex-1 to the
  h2 so long titles shrink instead of pushing the delete button away.
- Normalize the headword in FrequencyRankTable before comparing it to
  the (hiragana-normalized) reading so katakana-only entries like カレー
  no longer render a redundant 【かれー】. Test strengthened to reject
  any bracketed reading, not just the literal.
- Rewrite confirmBucketDelete copy to include the "and all associated
  data" warning and handle singular/plural cleanly.
- Run Prettier across the stats files CI was complaining about
  (EpisodeDetail, WatchTimeChart, SessionsTab + test, FrequencyRankTable
  + test, session-grouping test) to clear the format:check:stats gate.

stats/src/components/anime/EpisodeDetail.tsx

@@ -184,7 +184,8 @@ export function EpisodeDetail({ videoId, onSessionDeleted }: EpisodeDetailProps)
           </div>
           {hiddenCardCount > 0 && (
             <div className="px-3 pb-3 -mt-1 text-[10px] text-ctp-overlay2 italic">
-              {hiddenCardCount} {hiddenCardCount === 1 ? 'card' : 'cards'} hidden (deleted from Anki)
+              {hiddenCardCount} {hiddenCardCount === 1 ? 'card' : 'cards'} hidden (deleted from
+              Anki)
             </div>
           )}
         </div>