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/main.tsx

@@ -0,0 +1,18 @@
+import { StrictMode } from 'react';
+import { createRoot } from 'react-dom/client';
+import { App } from './App';
+import './styles/globals.css';
+
+const isOverlay = new URLSearchParams(window.location.search).has('overlay');
+if (isOverlay) {
+  document.body.classList.add('overlay-mode');
+}
+
+const root = document.getElementById('root');
+if (root) {
+  createRoot(root).render(
+    <StrictMode>
+      <App />
+    </StrictMode>
+  );
+}