Keep e621 metadata on downloaded posts; clear up account roles

Roles:
- JakeBreathild is now staff + superuser (the real account); the 'jake'
  smoke-test account was demoted to a regular user
- /me exposes is_superuser and the account page shows an admin badge

e621 metadata:
- MediaItem gains e621_post_id and e621_data (trimmed post payload:
  tags by category, rating, score, favourites, comments, sources,
  description, pools, relationships, file info, uploader)
- Download to Library accepts the post payload from the SPA and stores
  it; the item's custom rating is seeded from the e621 rating when empty
- Library detail shows an e621 metadata card: link to the in-app post,
  score/favourites/comments, taxonomy-coloured tags, DText description,
  sources and pools; grid cards get an e621 badge and fall back to the
  e621 rating for their colour (display_rating)
- Guest visibility now also considers e621 tags, so downloaded explicit
  content is hidden from anonymous visitors

frontend/src/components/MediaCard.tsx

@@ -21,6 +21,7 @@ export function MediaCard({ item }: { item: MediaItem }) {
     item.kind === "video"
       ? `/api/files/${item.j_id}/thumbnail/`
       : `/api/files/${item.j_id}/raw/`;
+  const rating = item.display_rating;
 
   return (
     <Link
@@ -34,14 +35,22 @@ export function MediaCard({ item }: { item: MediaItem }) {
           loading="lazy"
           className="h-full w-full object-cover transition duration-200 group-hover:scale-[1.03]"
         />
-        {item.rating ? (
+        {rating ? (
           <span
             className={cn(
               "absolute left-2 top-2 rounded-full border px-2 py-0.5 font-mono text-[11px] font-medium",
-              ratingStyles[item.rating],
+              ratingStyles[rating],
             )}
           >
-            {ratingLabels[item.rating]}
+            {ratingLabels[rating]}
+          </span>
+        ) : null}
+        {item.e621_post_id ? (
+          <span
+            className="absolute left-2 top-8 rounded-sm bg-ctp-lavender/90 px-1.5 py-0.5 font-mono text-[10px] font-medium text-ctp-crust"
+            title={`e621 post #${item.e621_post_id}`}
+          >
+            e621
           </span>
         ) : null}
         <span className="absolute right-2 top-2 rounded-sm bg-ctp-crust/80 px-1.5 py-0.5 font-mono text-[10px] uppercase text-ctp-overlay1">

frontend/src/components/TagChip.tsx

@@ -33,17 +33,19 @@ export function TagChip({
   onClick?: () => void;
 }) {
   const style = TAG_STYLES[category ?? "unknown"] ?? TAG_STYLES.unknown;
+  const className = cn(
+    "rounded border px-1.5 py-0.5 font-mono text-[11px] transition",
+    style,
+  );
+  const label = count !== undefined ? `${tag} (${count})` : tag;
+
+  if (!onClick) {
+    return <span className={className}>{label}</span>;
+  }
+
   return (
-    <button
-      type="button"
-      onClick={onClick}
-      className={cn(
-        "rounded border px-1.5 py-0.5 font-mono text-[11px] transition",
-        style,
-      )}
-    >
-      {tag}
-      {count !== undefined ? ` (${count})` : ""}
+    <button type="button" onClick={onClick} className={className}>
+      {label}
     </button>
   );
 }