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/App.tsx

@@ -1,14 +1,20 @@
 import { useEffect, type ReactNode } from "react";
-import { Navigate, Route, Routes, useLocation } from "react-router-dom";
+import {
+  Navigate,
+  Route,
+  Routes,
+  useLocation,
+  useParams,
+} from "react-router-dom";
 
 import { AppShell } from "@/components/AppShell";
 import { FullPageSpinner } from "@/components/ui";
 import AccountPage from "@/features/account/AccountPage";
 import LoginPage from "@/features/auth/LoginPage";
 import RegisterPage from "@/features/auth/RegisterPage";
-import FileDetailPage from "@/features/library/FileDetailPage";
+import DetailPage from "@/features/detail/DetailPage";
 import LibraryPage from "@/features/library/LibraryPage";
-import OnlineDetailPage from "@/features/online/OnlineDetailPage";
+import Md5Redirect from "@/features/library/Md5Redirect";
 import OnlinePage from "@/features/online/OnlinePage";
 import UploadPage from "@/features/upload/UploadPage";
 import { useAuth } from "@/store/auth";
@@ -22,6 +28,11 @@ function RequireAuth({ children }: { children: ReactNode }) {
   return <>{children}</>;
 }
 
+function PostRedirect() {
+  const { postId = "" } = useParams();
+  return <Navigate to={`/detail/${postId}`} replace />;
+}
+
 export default function App() {
   const ready = useAuth((state) => state.ready);
   const loadUser = useAuth((state) => state.loadUser);
@@ -38,9 +49,10 @@ export default function App() {
     <Routes>
       <Route element={<AppShell />}>
         <Route path="/" element={<LibraryPage />} />
-        <Route path="/view/:md5" element={<FileDetailPage />} />
+        <Route path="/detail/:itemId" element={<DetailPage />} />
+        <Route path="/view/:md5" element={<Md5Redirect />} />
         <Route path="/online" element={<OnlinePage />} />
-        <Route path="/online/view/:id" element={<OnlineDetailPage />} />
+        <Route path="/online/view/:postId" element={<PostRedirect />} />
         <Route
           path="/upload"
           element={