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/lib/types.ts

@@ -3,6 +3,7 @@ export interface User {
   username: string;
   email: string;
   is_staff: boolean;
+  is_superuser: boolean;
   date_joined: string;
   role: "user" | "uploader" | "staff";
   can_upload: boolean;
@@ -19,12 +20,42 @@ export interface MediaLocation {
 
 export type Rating = "" | "s" | "q" | "e";
 
+export interface E621StoredPost {
+  id: number | null;
+  created_at?: string | null;
+  rating?: "s" | "q" | "e" | null;
+  tags: Record<string, string[]>;
+  score?: {
+    up?: number | null;
+    down?: number | null;
+    total?: number | null;
+  } | null;
+  fav_count?: number | null;
+  comment_count?: number | null;
+  sources: string[];
+  description: string;
+  pools: number[];
+  relationships?: {
+    parent_id?: number | null;
+    has_children?: boolean | null;
+  } | null;
+  file?: {
+    md5?: string | null;
+    ext?: string | null;
+    size?: number | null;
+    width?: number | null;
+    height?: number | null;
+  } | null;
+  uploader_name?: string | null;
+}
+
 export interface MediaItem {
   id: number;
   j_id: string;
   md5: string;
   size: number;
   rating: Rating;
+  display_rating: Rating;
   tags: string[];
   notes: string;
   filename: string;
@@ -32,6 +63,8 @@ export interface MediaItem {
   kind: "image" | "video";
   uploaded_by: string | null;
   uploaded_by_id: number | null;
+  e621_post_id: number | null;
+  e621_data: E621StoredPost | null;
   locations: MediaLocation[];
   created_at: string;
   updated_at: string;