feat(stats): add library entry merge and episode move

- Add multi-select "Merge Selected" flow to fold duplicate library cards into one, preserving sessions, mined cards, and watch time
- Add per-episode "move to another entry" action for reassigning stray episodes, pruning the source entry when emptied
- Auto-merge library entries that resolve to the same AniList id when their parsed seasons are compatible
- Add mergeAnime/moveVideoToAnime service methods, stats-server routes, and HTTP contract types

stats/src/components/anime/AnimeCard.tsx

@@ -5,22 +5,45 @@ import type { AnimeLibraryItem } from '../../types/stats';
 interface AnimeCardProps {
   anime: AnimeLibraryItem;
   onClick: () => void;
+  /** While selecting, clicking the card toggles it instead of opening it. */
+  selectable?: boolean;
+  selected?: boolean;
 }
 
-export function AnimeCard({ anime, onClick }: AnimeCardProps) {
+export function AnimeCard({
+  anime,
+  onClick,
+  selectable = false,
+  selected = false,
+}: AnimeCardProps) {
   return (
     <button
       type="button"
       onClick={onClick}
-      className="group bg-ctp-surface0 border border-ctp-surface1 rounded-lg overflow-hidden hover:border-ctp-blue/50 hover:shadow-lg hover:shadow-ctp-blue/10 transition-all duration-200 hover:-translate-y-1 text-left w-full"
+      aria-pressed={selectable ? selected : undefined}
+      className={`group bg-ctp-surface0 border rounded-lg overflow-hidden hover:shadow-lg hover:shadow-ctp-blue/10 transition-all duration-200 hover:-translate-y-1 text-left w-full ${
+        selected ? 'border-ctp-blue' : 'border-ctp-surface1 hover:border-ctp-blue/50'
+      }`}
     >
-      <div className="overflow-hidden">
+      <div className="overflow-hidden relative">
         <AnimeCoverImage
           animeId={anime.animeId}
           title={anime.canonicalTitle}
           coverRetryToken={anime.anilistId ?? 0}
           className="w-full aspect-[3/4] rounded-t-lg transition-transform duration-200 group-hover:scale-105"
         />
+        {selectable && (
+          <span
+            aria-hidden="true"
+            className={`absolute top-2 left-2 w-5 h-5 rounded border flex items-center justify-center text-xs ${
+              selected
+                ? 'bg-ctp-blue border-ctp-blue text-ctp-base'
+                : 'bg-ctp-crust/70 border-ctp-surface2 text-transparent'
+            }`}
+          >
+            {'✓'}
+          </span>
+        )}
       </div>
       <div className="p-3">
         <div className="text-sm font-medium text-ctp-text truncate">{anime.canonicalTitle}</div>