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/overview/OverviewTab.tsx

@@ -0,0 +1,80 @@
+import { useOverview } from '../../hooks/useOverview';
+import { useStreakCalendar } from '../../hooks/useStreakCalendar';
+import { HeroStats } from './HeroStats';
+import { StreakCalendar } from './StreakCalendar';
+import { RecentSessions } from './RecentSessions';
+import { TrendChart } from '../trends/TrendChart';
+import { buildOverviewSummary, buildStreakCalendar } from '../../lib/dashboard-data';
+import { formatNumber } from '../../lib/formatters';
+
+export function OverviewTab() {
+  const { data, sessions, loading, error } = useOverview();
+  const { calendar, loading: calLoading } = useStreakCalendar(90);
+
+  if (loading) return <div className="text-ctp-overlay2 p-4">Loading...</div>;
+  if (error) return <div className="text-ctp-red p-4">Error: {error}</div>;
+  if (!data) return null;
+
+  const summary = buildOverviewSummary(data);
+  const streakData = buildStreakCalendar(calendar);
+  const showTrackedCardNote = summary.totalTrackedCards === 0 && summary.totalSessions > 0;
+
+  return (
+    <div className="space-y-4">
+      <HeroStats summary={summary} sessions={sessions} />
+
+      <div className="grid grid-cols-1 md:grid-cols-2 gap-4">
+        <TrendChart
+          title="Last 14 Days Watch Time (min)"
+          data={summary.recentWatchTime}
+          color="#8aadf4"
+          type="bar"
+        />
+        {!calLoading && <StreakCalendar data={streakData} />}
+      </div>
+
+      <div className="bg-ctp-surface0 border border-ctp-surface1 rounded-lg p-4">
+        <h3 className="text-sm font-semibold text-ctp-text mb-3">Tracking Snapshot</h3>
+        {showTrackedCardNote && (
+          <div className="mb-3 rounded-lg border border-ctp-surface2 bg-ctp-surface1/50 px-3 py-2 text-xs text-ctp-subtext0">
+            No tracked card-add events in the current immersion DB yet. New cards mined after this fix will show here.
+          </div>
+        )}
+        <div className="grid grid-cols-2 sm:grid-cols-5 gap-3 text-sm">
+          <div className="rounded-lg bg-ctp-surface1/60 p-3">
+            <div className="text-xs uppercase tracking-wide text-ctp-overlay2">Total Sessions</div>
+            <div className="mt-1 text-xl font-semibold text-ctp-lavender">
+              {formatNumber(summary.totalSessions)}
+            </div>
+          </div>
+          <div className="rounded-lg bg-ctp-surface1/60 p-3">
+            <div className="text-xs uppercase tracking-wide text-ctp-overlay2">Episodes Today</div>
+            <div className="mt-1 text-xl font-semibold text-ctp-teal">
+              {formatNumber(summary.episodesToday)}
+            </div>
+          </div>
+          <div className="rounded-lg bg-ctp-surface1/60 p-3">
+            <div className="text-xs uppercase tracking-wide text-ctp-overlay2">All-Time Hours</div>
+            <div className="mt-1 text-xl font-semibold text-ctp-mauve">
+              {formatNumber(summary.allTimeHours)}
+            </div>
+          </div>
+          <div className="rounded-lg bg-ctp-surface1/60 p-3">
+            <div className="text-xs uppercase tracking-wide text-ctp-overlay2">Active Days</div>
+            <div className="mt-1 text-xl font-semibold text-ctp-peach">
+              {formatNumber(summary.activeDays)}
+            </div>
+          </div>
+          <div className="rounded-lg bg-ctp-surface1/60 p-3">
+            <div className="text-xs uppercase tracking-wide text-ctp-overlay2">Cards Mined</div>
+            <div className="mt-1 text-xl font-semibold text-ctp-green">
+              {formatNumber(summary.totalTrackedCards)}
+            </div>
+          </div>
+        </div>
+      </div>
+
+      <RecentSessions sessions={sessions} />
+    </div>
+  );
+}