Duplicates, delete & storage, users page with J-ID avatars

Backend:
- Perceptual hashes (aHash/dHash/pHash/wHash via imagehash, no imgdd)
  stored on items, computed on upload/download and by the new
  compute_visual_hashes command
- Duplicates API: exact duplicates (multi-location items), visual matches
  for one item, union-find similarity groups with pagination
- Delete API with ownership/staff checks, per-item and per-copy deletion,
  watched-folder path validation; storage overview and temp cleanup;
  file list accepts j_ids batches
- Staged uploads are flagged visual_match with their library matches
  (threshold via VISUAL_MATCH_THRESHOLD)
- Staff users API: list with upload counts, set role and avatar by J-ID;
  User.avatar FK with signed avatar URLs
- Download threads close their DB connection and stale tasks are reaped,
  keeping behaviour Gunicorn-friendly

Frontend:
- /duplicates: exact duplicate groups with per-copy delete, visual
  similarity controls, search similar to a J-ID, paginated groups with
  selection, bulk delete and dismiss
- /delete: storage cards, delete by J-ID with preview grid, temp cleanup
- /users: staff directory with role selects and avatar J-ID inputs
- Nav + command palette entries; top-bar avatar; upload cards and the
  metadata modal show library visual matches

frontend/src/lib/types.ts

@@ -7,10 +7,70 @@ export interface User {
   date_joined: string;
   role: "user" | "uploader" | "staff";
   can_upload: boolean;
+  avatar_j_id: string | null;
+  avatar_url: string | null;
   e621_username: string;
   e621_configured: boolean;
 }
 
+export interface AdminUser {
+  id: number;
+  username: string;
+  email: string;
+  role: "user" | "uploader" | "staff";
+  is_staff: boolean;
+  is_superuser: boolean;
+  date_joined: string;
+  avatar_j_id: string | null;
+  avatar_url: string | null;
+  uploads_count: number;
+}
+
+export interface DuplicateEntry {
+  j_id: string;
+  md5: string;
+  filename: string;
+  size: number;
+  rating: string;
+  location_count: number;
+  uploaded_by: string | null;
+  e621_post_id: number | null;
+  locations?: { id: number; rel_path: string }[];
+  similarity?: number;
+}
+
+export interface VisualGroupsResponse {
+  count: number;
+  page: number;
+  per_page: number;
+  has_next: boolean;
+  threshold: number;
+  algorithms: string[];
+  groups: { size: number; members: DuplicateEntry[] }[];
+}
+
+export interface VisualMatchesResponse {
+  target: DuplicateEntry;
+  threshold: number;
+  algorithms: string[];
+  count: number;
+  matches: DuplicateEntry[];
+}
+
+export interface StorageInfo {
+  watched_folder: {
+    path: string;
+    total: number;
+    used: number;
+    free: number;
+    library_size: number;
+    percent_used: number;
+  };
+  media: { path: string; size: number };
+  temp: { path: string; size: number; files: number };
+  library_items: number;
+}
+
 export interface MediaLocation {
   id: number;
   path: string;
@@ -148,6 +208,9 @@ export interface TempUpload {
   custom_tags: string[];
   custom_notes: string;
   iqdb_data: E621IqdbCandidate[] | null;
+  visual_matches:
+    | { j_id: string; filename: string; similarity: number }[]
+    | null;
   library_j_id: string | null;
   file_url: string | null;
   preview_url: string | null;