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

changes/fix-stats-cover-refresh.md

@@ -0,0 +1,4 @@
+type: fixed
+area: stats
+
+- Retried and batched stats home cover images from stored DB art so AniList art appears without extra AniList lookups or a full page refresh.

changes/overlay-mining-image-toast.md

@@ -0,0 +1,4 @@
+type: added
+area: overlay
+
+- Show a screenshot of the mined frame as an in-overlay image toast alongside the OSD card-mining notification, matching the picture already shown on system notifications.

changes/stats-delete-progress-indicator.md

@@ -0,0 +1,4 @@
+type: added
+area: stats
+
+- Showed a progress indicator while sessions are being deleted on the home and sessions pages, so long batch deletes give visible feedback instead of appearing to do nothing.

changes/stats-session-delete-speed.md

@@ -0,0 +1,4 @@
+type: fixed
+area: stats
+
+- Sped up deleting stats sessions by refreshing only affected rollups and rebuilding lifetime summaries with aggregate SQL.