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/sessions/SessionsTab.tsx

@@ -269,9 +269,7 @@ export function SessionsTab({
                                 isExpanded={expandedId === s.sessionId}
                                 detailsId={detailsId}
                                 onToggle={() =>
-                                  setExpandedId(
-                                    expandedId === s.sessionId ? null : s.sessionId,
-                                  )
+                                  setExpandedId(expandedId === s.sessionId ? null : s.sessionId)
                                 }
                                 onDelete={() => void handleDeleteSession(s)}
                                 deleteDisabled={deletingSessionId === s.sessionId}