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/components/vocabulary/KanjiBreakdown.tsx

@@ -0,0 +1,46 @@
+import type { KanjiEntry } from '../../types/stats';
+
+interface KanjiBreakdownProps {
+  kanji: KanjiEntry[];
+  selectedKanjiId?: number | null;
+  onSelectKanji?: (entry: KanjiEntry) => void;
+}
+
+export function KanjiBreakdown({
+  kanji,
+  selectedKanjiId = null,
+  onSelectKanji,
+}: KanjiBreakdownProps) {
+  if (kanji.length === 0) return null;
+
+  const maxFreq = kanji.reduce((max, entry) => Math.max(max, entry.frequency), 1);
+
+  return (
+    <div className="bg-ctp-surface0 border border-ctp-surface1 rounded-lg p-4">
+      <h3 className="text-sm font-semibold text-ctp-text mb-3">Kanji Encountered</h3>
+      <div className="flex flex-wrap gap-1">
+        {kanji.map((k) => {
+          const ratio = k.frequency / maxFreq;
+          const opacity = Math.max(0.3, ratio);
+          return (
+            <button
+              type="button"
+              key={k.kanji}
+              className={`cursor-pointer rounded px-1 text-lg text-ctp-teal transition ${
+                selectedKanjiId === k.kanjiId
+                  ? 'bg-ctp-teal/10 ring-1 ring-ctp-teal'
+                  : 'hover:bg-ctp-surface1/80'
+              }`}
+              style={{ opacity }}
+              title={`${k.kanji} — seen ${k.frequency}x`}
+              aria-label={`${k.kanji} — seen ${k.frequency} times`}
+              onClick={() => onSelectKanji?.(k)}
+            >
+              {k.kanji}
+            </button>
+          );
+        })}
+      </div>
+    </div>
+  );
+}