feat(stats): build anime-centric stats dashboard frontend

5-tab React dashboard with Catppuccin Mocha theme:
- Overview: hero stats, streak calendar, watch time chart, recent sessions
- Anime: grid with cover art, episode list with completion %, detail view
- Trends: 15 charts across Activity, Efficiency, Anime, and Patterns
- Vocabulary: POS-filtered word/kanji lists with detail panels
- Sessions: expandable session history with event timeline

Features:
- Cross-tab navigation (anime <-> vocabulary)
- Global word detail panel overlay
- Expandable episode detail with Anki card links (Expression field)
- Per-anime multi-line trend charts
- Watch time by day-of-week and hour-of-day
- Collapsible sections with accessibility (aria-expanded)
- Card size selector for anime grid
- Cover art caching via AniList
- HTTP API client with file:// protocol fallback for Electron overlay

stats/src/hooks/useStreakCalendar.ts

@@ -0,0 +1,21 @@
+import { useState, useEffect } from 'react';
+import { getStatsClient } from './useStatsApi';
+import type { StreakCalendarDay } from '../types/stats';
+
+export function useStreakCalendar(days = 90) {
+  const [calendar, setCalendar] = useState<StreakCalendarDay[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+
+  useEffect(() => {
+    let cancelled = false;
+    getStatsClient()
+      .getStreakCalendar(days)
+      .then((data) => { if (!cancelled) setCalendar(data); })
+      .catch((err: Error) => { if (!cancelled) setError(err.message); })
+      .finally(() => { if (!cancelled) setLoading(false); });
+    return () => { cancelled = true; };
+  }, [days]);
+
+  return { calendar, loading, error };
+}