Phase 3: J-IDs, ownership, roles, guest safety, adaptive detail, download

Backend:
- User.role (user/uploader/staff) with can_upload; uploads and downloads
  gated to uploader+; owners and staff can edit their items
- MediaItem.uploaded_by plus J-<id> identity (serializer, admin,
  scan_files --user, first superuser as default owner)
- API resolves J-<id>, bare numeric ids and MD5s; neighbors and lookup
  return j_ids
- Guest safety: mirror e621's anonymous default blacklist into Redis
  (parses comments, negations and wildcards), flag hidden_from_guests
  and filter lists, details and lookups for anonymous users
- POST /api/online/downloads/ writes an e621 file into the watched
  folder and indexes it for the uploader
- MariaDB + Redis via docker compose (host ports 3307/6380), PyMySQL
  driver shim, Redis cache replacing the file cache; SQLite data
  dumped and loaded into MariaDB

Frontend:
- Single /detail/:itemId route with an adaptive shell: J-<id> renders
  the library item, bare numbers render the e621 post
- Legacy /view/<md5> and /online/view/<id> redirect to canonical URLs
- Cards expose J-IDs; library custom-data editor is read-only for
  non-owners
- Role gating: Upload hidden/blocked for regular users, account shows
  the role, guest hint on the library

frontend/src/features/account/AccountPage.tsx

@@ -230,8 +230,11 @@ export default function AccountPage() {
       <header>
         <h1 className="text-lg font-semibold">Account</h1>
         {user ? (
-          <p className="mt-1 text-sm text-ctp-overlay0">
-            Signed in as {user.username}.
+          <p className="mt-1 flex items-center gap-2 text-sm text-ctp-overlay0">
+            <span>Signed in as {user.username}.</span>
+            <span className="rounded-full border border-ctp-surface1 px-2 py-0.5 font-mono text-[11px] capitalize text-ctp-subtext0">
+              {user.role}
+            </span>
           </p>
         ) : null}
       </header>