fix(stats): fix data loss and error handling in anime merge/move

- flush pending telemetry before merge/move so in-progress session time isn't dropped from lifetime totals
- repoint subtitle lines by video_id instead of anime_id so lines recorded before the async title parse assigns a link aren't stranded
- stop absorbing metadata into the target when moving an episode out of an emptied entry (a move isn't a same-show claim)
- return 404 only for missing episode/target, not storage failures; return 404 when a merge folds nothing
- keep AnimeMergeDialog open while a merge is in flight instead of letting dismiss race the request
- surface library load failures in LibraryEntryPicker instead of showing an empty list

stats/src/components/anime/AnimeMergeDialog.tsx

@@ -43,8 +43,18 @@ export function AnimeMergeDialog({ entries, onClose, onMerged }: AnimeMergeDialo
     }
   };
 
+  // Dismissing mid-request would leave the caller unaware of a merge that is
+  // still going to land, so the backdrop and close button are inert until it
+  // resolves.
+  const handleDismiss = () => {
+    if (!merging) onClose();
+  };
+
   return (
-    <div className="fixed inset-0 z-50 flex items-start justify-center pt-[10vh]" onClick={onClose}>
+    <div
+      className="fixed inset-0 z-50 flex items-start justify-center pt-[10vh]"
+      onClick={handleDismiss}
+    >
       <div className="absolute inset-0 bg-ctp-crust/70 backdrop-blur-[2px]" />
       <div
         className="relative bg-ctp-base border border-ctp-surface1 rounded-xl shadow-2xl w-full max-w-lg max-h-[70vh] flex flex-col animate-fade-in"
@@ -57,8 +67,9 @@ export function AnimeMergeDialog({ entries, onClose, onMerged }: AnimeMergeDialo
             </h3>
             <button
               type="button"
-              onClick={onClose}
-              className="text-ctp-overlay2 hover:text-ctp-text text-lg leading-none"
+              onClick={handleDismiss}
+              disabled={merging}
+              className="text-ctp-overlay2 hover:text-ctp-text text-lg leading-none disabled:opacity-50"
             >
               {'✕'}
             </button>

stats/src/components/anime/EpisodeList.tsx

@@ -205,7 +205,7 @@ export function EpisodeList({
                             setMoveError(null);
                             setMovingEpisode(ep);
                           }}
-                          className={`w-5 h-5 rounded border border-ctp-surface2 text-transparent hover:border-ctp-blue/50 hover:text-ctp-blue hover:bg-ctp-blue/10 transition-colors text-xs flex items-center justify-center ${HOVER_REVEALED}`}
+                          className={`w-5 h-5 rounded border border-ctp-surface2 text-transparent hover:border-ctp-blue/50 hover:text-ctp-blue focus-visible:text-ctp-blue hover:bg-ctp-blue/10 transition-colors text-xs flex items-center justify-center ${HOVER_REVEALED}`}
                           title="Move to another library entry"
                           aria-label="Move to another library entry"
                         >
@@ -217,7 +217,7 @@ export function EpisodeList({
                             e.stopPropagation();
                             void handleDeleteEpisode(ep.videoId, ep.canonicalTitle);
                           }}
-                          className={`w-5 h-5 rounded border border-ctp-surface2 text-transparent hover:border-ctp-red/50 hover:text-ctp-red hover:bg-ctp-red/10 transition-colors text-xs flex items-center justify-center ${HOVER_REVEALED}`}
+                          className={`w-5 h-5 rounded border border-ctp-surface2 text-transparent hover:border-ctp-red/50 hover:text-ctp-red focus-visible:text-ctp-red hover:bg-ctp-red/10 transition-colors text-xs flex items-center justify-center ${HOVER_REVEALED}`}
                           title="Delete episode"
                           aria-label="Delete episode"
                         >

stats/src/components/anime/LibraryEntryPicker.tsx

@@ -25,6 +25,7 @@ export function LibraryEntryPicker({
   onClose,
 }: LibraryEntryPickerProps) {
   const [entries, setEntries] = useState<AnimeLibraryItem[] | null>(null);
+  const [loadFailed, setLoadFailed] = useState(false);
   const [query, setQuery] = useState(initialQuery);
   const inputRef = useRef<HTMLInputElement>(null);
 
@@ -37,7 +38,11 @@ export function LibraryEntryPicker({
         if (!cancelled) setEntries(data);
       })
       .catch(() => {
-        if (!cancelled) setEntries([]);
+        // Distinct from an empty library: telling the user "no other titles"
+        // when the request failed hides a retryable error.
+        if (cancelled) return;
+        setEntries([]);
+        setLoadFailed(true);
       });
     return () => {
       cancelled = true;
@@ -84,7 +89,12 @@ export function LibraryEntryPicker({
 
         <div className="flex-1 overflow-y-auto p-2">
           {entries === null && <div className="text-xs text-ctp-overlay2 p-3">Loading...</div>}
-          {entries !== null && visible.length === 0 && (
+          {loadFailed && (
+            <div className="text-xs text-ctp-red p-3">
+              Could not load the library. Close this dialog and try again.
+            </div>
+          )}
+          {!loadFailed && entries !== null && visible.length === 0 && (
             <div className="text-xs text-ctp-overlay2 p-3">No other titles</div>
           )}
           {visible.map((entry) => (