Fix hidden library items not rendering in the browser

Items flagged hidden_from_guests (blacklisted tags) returned 404 for
<img> requests since tags cannot send the auth header. The API now
exposes signed raw_url/thumbnail_url fields (mirroring upload previews
and avatars), and the SPA uses them in the gallery, detail view,
duplicates and delete screens, and upload visual matches.

frontend/src/features/library/DeletePage.tsx

@@ -229,7 +229,7 @@ export default function DeletePage() {
                   >
                     <div className="relative aspect-square overflow-hidden bg-ctp-mantle">
                       <img
-                        src={`/api/files/${item.j_id}/thumbnail/`}
+                        src={item.thumbnail_url}
                         alt={item.filename}
                         loading="lazy"
                         className="h-full w-full object-cover"

frontend/src/features/library/DuplicatesPage.tsx

@@ -33,6 +33,8 @@ function MemberCard({
   selected: boolean;
   onToggle: () => void;
 }) {
+  const preview =
+    entry.thumbnail_url ?? `/api/files/${entry.j_id}/thumbnail/`;
   return (
     <div
       className={cn(
@@ -43,7 +45,7 @@ function MemberCard({
       <button type="button" onClick={onToggle} className="block w-full text-left">
         <div className="relative aspect-square overflow-hidden bg-ctp-mantle">
           <img
-            src={`/api/files/${entry.j_id}/thumbnail/`}
+            src={preview}
             alt={entry.j_id}
             loading="lazy"
             className="h-full w-full object-cover"
@@ -219,7 +221,10 @@ export default function DuplicatesPage() {
                 <div className="w-32 shrink-0">
                   <div className="aspect-square overflow-hidden rounded-md bg-ctp-mantle">
                     <img
-                      src={`/api/files/${group.j_id}/thumbnail/`}
+                      src={
+                        group.thumbnail_url ??
+                        `/api/files/${group.j_id}/thumbnail/`
+                      }
                       alt={group.j_id}
                       loading="lazy"
                       className="h-full w-full object-cover"

frontend/src/features/library/LibraryDetail.tsx

@@ -300,13 +300,17 @@ export function LibraryDetail({ jId }: { jId: string }) {
   const ordering = useUi((state) => state.ordering);
   const user = useAuth((state) => state.user);
   const [confirmDelete, setConfirmDelete] = useState(false);
-  const rawUrl = `/api/files/${jId}/raw/`;
 
   const query = useQuery({
     queryKey: ["file", jId],
     queryFn: () => api<MediaItem>(`/api/files/${jId}/`),
   });
 
+  const rawUrl = query.data?.raw_url ?? `/api/files/${jId}/raw/`;
+  const downloadUrl = rawUrl.includes("?")
+    ? `${rawUrl}&download=1`
+    : `${rawUrl}?download=1`;
+
   const neighborsQuery = useQuery({
     queryKey: ["neighbors", jId, ordering],
     queryFn: () =>
@@ -335,7 +339,7 @@ export function LibraryDetail({ jId }: { jId: string }) {
       if (isTypingTarget(event.target)) return;
       if (event.key === "d" || event.key === "D") {
         event.preventDefault();
-        window.location.href = `${rawUrl}?download=1`;
+        window.location.href = downloadUrl;
         return;
       }
       const neighbors = neighborsQuery.data;
@@ -347,7 +351,7 @@ export function LibraryDetail({ jId }: { jId: string }) {
     }
     window.addEventListener("keydown", handleKeyDown);
     return () => window.removeEventListener("keydown", handleKeyDown);
-  }, [neighborsQuery.data, navigate, rawUrl]);
+  }, [neighborsQuery.data, navigate, downloadUrl]);
 
   if (query.isPending) {
     return (
@@ -400,7 +404,7 @@ export function LibraryDetail({ jId }: { jId: string }) {
       }
       actions={
         <div className="flex flex-wrap items-center gap-2">
-          <a href={`${rawUrl}?download=1`} className={linkButtonClass}>
+          <a href={downloadUrl} className={linkButtonClass}>
             <Download className="h-4 w-4" /> Download
           </a>
           {canDelete ? (

frontend/src/features/upload/UploadPage.tsx

@@ -385,7 +385,10 @@ function MetadataModal({
                           className="flex items-center gap-3 rounded-md border border-ctp-surface0 bg-ctp-surface0/40 p-2"
                         >
                           <img
-                            src={`/api/files/${match.j_id}/thumbnail/`}
+                            src={
+                              match.thumbnail_url ??
+                              `/api/files/${match.j_id}/thumbnail/`
+                            }
                             alt={match.j_id}
                             loading="lazy"
                             className="h-12 w-12 shrink-0 rounded object-cover"