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

ROADMAP.md

@@ -5,15 +5,16 @@ they land.
 
 ## 1. Library management
 
-- [ ] **Duplicates engine**
-  - [ ] Exact MD5 duplicate detection with grouped results
-  - [ ] Perceptual similarity (aHash, dHash, pHash, wHash) with threshold slider
-        and algorithm toggles (needs `imagehash`/`imgdd` server-side)
-  - [ ] Visual similarity groups: pagination, "keep one / delete rest", dismiss group
-- [ ] **Delete & storage page**
-  - [ ] Storage overview (watched folder, media folder)
-  - [ ] Delete by J-ID with preview grid and bulk selection
-  - [ ] Temp folder cleanup
+- [x] **Duplicates engine**
+  - [x] Exact MD5 duplicate detection with grouped results
+  - [x] Perceptual similarity (aHash, dHash, pHash, wHash) with threshold slider
+        and algorithm toggles (`imagehash` server-side)
+  - [x] Visual similarity groups: pagination, selection, delete and dismiss
+- [x] **Delete & storage page**
+  - [x] Storage overview (watched folder, media folder, temp)
+  - [x] Delete by J-ID with preview grid and bulk selection (plus per-copy
+        deletion of duplicate locations)
+  - [x] Temp folder cleanup
 - [ ] **Library search upgrades**
   - [ ] Search by tags (custom + e621 tags), not just filename
   - [ ] Tag cloud from the library
@@ -58,8 +59,8 @@ Files now stage first and are resolved before entering the library.
 - [x] **IQDB similarity on upload** (SPA-driven)
   - [x] Automatic + manual IQDB checks with candidate posts
   - [x] "Visual Similarity Detected" state with candidate picker
-  - [ ] Perceptual-hash comparison against the library (shared with the
-        duplicates engine, still pending)
+  - [x] Perceptual-hash comparison against the library (staged uploads are
+        flagged with their library matches as soon as they land)
 - [x] **Upload UI**
   - [x] Three-column board: Pending & Unmatched / Visual Similarity Detected /
         Auto-uploaded & Indexed
@@ -80,7 +81,8 @@ Files now stage first and are resolved before entering the library.
 
 - [ ] Toasts instead of inline messages / confirm dialogs
 - [ ] Mobile drawer polish for metadata panels (design spec §layout)
-- [ ] Avatar picker (choose from library)
+- [x] Profile pictures: staff Users page sets avatars from library J-IDs
+      (self-service picker in Account still pending)
 - [ ] Profile extras (per-user browse preferences)
 - [ ] Command palette: tag finder, recent searches