feat: show mining frame toast on OSD and speed up stats session deletes

- Flash mined-frame screenshot as in-overlay image toast for OSD card notifications
- Batch cover art from stored DB blobs via POST /api/stats/covers (no extra AniList fetches)
- Show delete progress toast on stats home and sessions pages
- Refresh only affected rollups on session delete instead of full rebuild
- Rebuild lifetime summaries with aggregate SQL CTEs instead of per-session loop

stats/src/components/overview/CoverThumbnail.tsx

@@ -0,0 +1,41 @@
+import { useEffect, useState } from 'react';
+import { getCoverImageSrc, type CoverImageMap } from '../../lib/cover-images';
+
+interface CoverThumbnailProps {
+  animeId: number | null;
+  videoId: number | null;
+  title: string;
+  coverImages: CoverImageMap;
+}
+
+export function CoverThumbnail({ animeId, videoId, title, coverImages }: CoverThumbnailProps) {
+  const [failed, setFailed] = useState(false);
+  const fallbackChar = title.charAt(0) || '?';
+  const fallback = (
+    <div className="w-12 h-16 rounded bg-ctp-surface2 flex items-center justify-center text-ctp-overlay2 text-lg font-bold shrink-0">
+      {fallbackChar}
+    </div>
+  );
+
+  const src =
+    animeId != null
+      ? getCoverImageSrc(coverImages, 'anime', animeId)
+      : getCoverImageSrc(coverImages, 'media', videoId);
+
+  useEffect(() => {
+    setFailed(false);
+  }, [src]);
+
+  if (!src || failed) {
+    return fallback;
+  }
+
+  return (
+    <img
+      src={src}
+      alt=""
+      className="w-12 h-16 rounded object-cover shrink-0 bg-ctp-surface2"
+      onError={() => setFailed(true)}
+    />
+  );
+}