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/AnimeTab.tsx

@@ -9,6 +9,7 @@ import {
 } from '../../lib/library-card-size';
 import { AnimeCard } from './AnimeCard';
 import { AnimeDetailView } from './AnimeDetailView';
+import { AnimeMergeDialog } from './AnimeMergeDialog';
 
 type SortKey = 'lastWatched' | 'watchTime' | 'cards' | 'episodes';
 
@@ -62,6 +63,21 @@ export function AnimeTab({
     ),
   );
   const [selectedAnimeId, setSelectedAnimeId] = useState<number | null>(null);
+  const [selectionMode, setSelectionMode] = useState(false);
+  const [checkedAnimeIds, setCheckedAnimeIds] = useState<number[]>([]);
+  const [showMergeDialog, setShowMergeDialog] = useState(false);
+
+  function toggleChecked(animeId: number): void {
+    setCheckedAnimeIds((ids) =>
+      ids.includes(animeId) ? ids.filter((id) => id !== animeId) : [...ids, animeId],
+    );
+  }
+
+  function exitSelectionMode(): void {
+    setSelectionMode(false);
+    setCheckedAnimeIds([]);
+    setShowMergeDialog(false);
+  }
 
   function handleCardSizeChange(size: LibraryCardSize): void {
     setCardSize(size);
@@ -86,6 +102,9 @@ export function AnimeTab({
   }, [anime, search, sortKey]);
 
   const totalMs = anime.reduce((sum, a) => sum + a.totalActiveMs, 0);
+  const checkedEntries = checkedAnimeIds
+    .map((animeId) => anime.find((entry) => entry.animeId === animeId))
+    .filter((entry): entry is (typeof anime)[number] => entry !== undefined);
 
   if (selectedAnimeId !== null) {
     return (
@@ -100,6 +119,7 @@ export function AnimeTab({
         }
         onAnimeDeleted={reload}
         onAnilistRelinked={reload}
+        onEpisodeMoved={reload}
       />
     );
   }
@@ -143,11 +163,41 @@ export function AnimeTab({
             </button>
           ))}
         </div>
+        <button
+          type="button"
+          onClick={() => (selectionMode ? exitSelectionMode() : setSelectionMode(true))}
+          title="Select several entries to merge them into one"
+          className={`px-2 py-2 rounded-lg border text-xs shrink-0 transition-colors ${
+            selectionMode
+              ? 'bg-ctp-blue/15 border-ctp-blue/40 text-ctp-blue'
+              : 'bg-ctp-surface0 border-ctp-surface1 text-ctp-overlay2 hover:text-ctp-subtext0'
+          }`}
+        >
+          {selectionMode ? 'Cancel' : 'Select'}
+        </button>
         <div className="text-xs text-ctp-overlay2 shrink-0">
           {filtered.length} titles · {formatDuration(totalMs)}
         </div>
       </div>
 
+      {selectionMode && (
+        <div className="flex items-center justify-between gap-3 bg-ctp-surface0 border border-ctp-surface1 rounded-lg px-3 py-2">
+          <div className="text-xs text-ctp-overlay2">
+            {checkedEntries.length === 0
+              ? 'Pick the duplicate entries to combine'
+              : `${checkedEntries.length} selected`}
+          </div>
+          <button
+            type="button"
+            disabled={checkedEntries.length < 2}
+            onClick={() => setShowMergeDialog(true)}
+            className="px-3 py-1.5 rounded-lg bg-ctp-blue/15 border border-ctp-blue/40 text-xs text-ctp-blue hover:bg-ctp-blue/25 transition-colors disabled:opacity-40 disabled:cursor-not-allowed"
+          >
+            Merge Selected
+          </button>
+        </div>
+      )}
+
       {filtered.length === 0 ? (
         <div className="text-sm text-ctp-overlay2 p-4">No titles found</div>
       ) : (
@@ -156,11 +206,26 @@ export function AnimeTab({
             <AnimeCard
               key={item.animeId}
               anime={item}
-              onClick={() => setSelectedAnimeId(item.animeId)}
+              selectable={selectionMode}
+              selected={checkedAnimeIds.includes(item.animeId)}
+              onClick={() =>
+                selectionMode ? toggleChecked(item.animeId) : setSelectedAnimeId(item.animeId)
+              }
             />
           ))}
         </div>
       )}
+
+      {showMergeDialog && checkedEntries.length >= 2 && (
+        <AnimeMergeDialog
+          entries={checkedEntries}
+          onClose={() => setShowMergeDialog(false)}
+          onMerged={() => {
+            exitSelectionMode();
+            reload();
+          }}
+        />
+      )}
     </div>
   );
 }