Add Transmission/NZBGet and per-client paths and much more

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.

tests/api/requests-approval.routes.test.ts

@@ -468,6 +468,7 @@ describe('Request Approval Workflow', () => {
           plexUsername: true,
           role: true,
           autoApproveRequests: true,
+          interactiveSearchAccess: true,
         },
       });
     });