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/components/AppShell.tsx

@@ -13,12 +13,6 @@ import { useAuth } from "@/store/auth";
 import { useE621 } from "@/store/e621";
 import { useUi } from "@/store/ui";
 
-const navItems = [
-  { to: "/", label: "Library" },
-  { to: "/online", label: "Online" },
-  { to: "/upload", label: "Upload" },
-];
-
 export function AppShell() {
   const user = useAuth((state) => state.user);
   const logout = useAuth((state) => state.logout);
@@ -63,6 +57,12 @@ export function AppShell() {
   const showSidebarToggle =
     location.pathname === "/" || location.pathname === "/online";
 
+  const navItems = [
+    { to: "/", label: "Library" },
+    { to: "/online", label: "Online" },
+    ...(user?.can_upload ? [{ to: "/upload", label: "Upload" }] : []),
+  ];
+
   const navigationType = useNavigationType();
   useEffect(() => {
     // New navigations start at the top; history back/forward keeps position.