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/overview/WatchTimeChart.tsx

@@ -1,13 +1,5 @@
 import { useState } from 'react';
-import {
-  BarChart,
-  Bar,
-  CartesianGrid,
-  XAxis,
-  YAxis,
-  Tooltip,
-  ResponsiveContainer,
-} from 'recharts';
+import { BarChart, Bar, CartesianGrid, XAxis, YAxis, Tooltip, ResponsiveContainer } from 'recharts';
 import { epochDayToDate } from '../../lib/formatters';
 import { CHART_DEFAULTS, CHART_THEME, TOOLTIP_CONTENT_STYLE } from '../../lib/chart-theme';
 import type { DailyRollup } from '../../types/stats';