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.
Extend multi-download-client support to include Transmission and NZBGet and introduce per-client custom download paths. Adds protocol mapping and new client types, Transmission/NZBGet integration services, API CRUD and validation changes, UI components/modal updates and live path previews, and manager routing by protocol. Includes DB migrations (download_path on download_history, interactive_search_access on users), schema updates, and related processor/service fixes and tests to ensure backward compatibility and proper path resolution.