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/lib/cover-images.ts

@@ -0,0 +1,72 @@
+import type { SessionSummary, StatsCoverImagesData } from '../types/stats';
+
+export type CoverImageKind = 'anime' | 'media';
+export type CoverImageMap = Record<string, string>;
+
+export interface CoverImageRequest {
+  animeIds: number[];
+  videoIds: number[];
+}
+
+function normalizePositiveIds(ids: Iterable<number | null | undefined>): number[] {
+  const uniqueIds = new Set<number>();
+  for (const id of ids) {
+    if (typeof id === 'number' && Number.isFinite(id) && id > 0) {
+      uniqueIds.add(Math.floor(id));
+    }
+  }
+  return Array.from(uniqueIds).sort((a, b) => a - b);
+}
+
+export function getCoverImageKey(kind: CoverImageKind, id: number): string {
+  return `${kind}:${id}`;
+}
+
+export function collectSessionCoverRequests(
+  sessions: Pick<SessionSummary, 'animeId' | 'videoId'>[],
+): CoverImageRequest {
+  const animeIds: number[] = [];
+  const videoIds: number[] = [];
+
+  for (const session of sessions) {
+    if (session.animeId != null) {
+      animeIds.push(session.animeId);
+    } else if (session.videoId != null) {
+      videoIds.push(session.videoId);
+    }
+  }
+
+  return {
+    animeIds: normalizePositiveIds(animeIds),
+    videoIds: normalizePositiveIds(videoIds),
+  };
+}
+
+export function mergeCoverImageData(
+  previous: CoverImageMap,
+  data: StatsCoverImagesData,
+): CoverImageMap {
+  const next = { ...previous };
+
+  for (const [id, image] of Object.entries(data.anime)) {
+    if (image?.dataUrl) {
+      next[getCoverImageKey('anime', Number(id))] = image.dataUrl;
+    }
+  }
+
+  for (const [id, image] of Object.entries(data.media)) {
+    if (image?.dataUrl) {
+      next[getCoverImageKey('media', Number(id))] = image.dataUrl;
+    }
+  }
+
+  return next;
+}
+
+export function getCoverImageSrc(
+  images: CoverImageMap,
+  kind: CoverImageKind,
+  id: number | null,
+): string | null {
+  return id == null ? null : (images[getCoverImageKey(kind, id)] ?? null);
+}