Add manual-import and download-access features

Introduce manual import workflow and download permission support. Adds a Prisma migration and schema field (users.download_access) to track per-user download access, and updates admin UI to toggle global and per-user download access. Implements new APIs: filesystem browse, manual-import endpoint, download-access settings, audiobook download-status, and on-demand download-token generation. Adds frontend components for manual import and related tests, plus documentation for the manual-import feature and the documentation-agent prompt. Key files: prisma/migrations/20260212000000_add_download_access_permission/migration.sql, prisma/schema.prisma, src/app/api/admin/filesystem/browse/route.ts, src/app/api/admin/manual-import/route.ts, src/app/api/admin/settings/download-access/route.ts, src/app/api/requests/[id]/download-token/route.ts, src/app/api/audiobooks/[asin]/download-status/route.ts, and updated admin users pages/components and permissions util.

src/app/api/auth/me/route.ts

@@ -39,6 +39,7 @@ export async function GET(request: NextRequest) {
         createdAt: true,
         lastLoginAt: true,
         interactiveSearchAccess: true,
+        downloadAccess: true,
       },
     });
 
@@ -63,6 +64,13 @@ export async function GET(request: NextRequest) {
       globalInteractiveSearch
     );
 
+    const globalDownload = await getGlobalBooleanSetting('download_access', true);
+    const effectiveDownload = resolvePermission(
+      user.role,
+      user.downloadAccess,
+      globalDownload
+    );
+
     return NextResponse.json({
       user: {
         id: user.id,
@@ -77,6 +85,7 @@ export async function GET(request: NextRequest) {
         lastLoginAt: user.lastLoginAt,
         permissions: {
           interactiveSearch: effectiveInteractiveSearch,
+          download: effectiveDownload,
         },
       },
     });