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-actions.routes.test.ts

@@ -79,6 +79,10 @@ describe('Request action routes', () => {
       userId: 'user-1',
       audiobook: { title: 'Title', author: 'Author' },
     });
+    prismaMock.user.findUnique.mockResolvedValueOnce({
+      role: 'user',
+      interactiveSearchAccess: null,
+    });
     configServiceMock.get.mockResolvedValueOnce(JSON.stringify([{ id: 1, priority: 10 }]));
     configServiceMock.get.mockResolvedValueOnce(null);
     prowlarrMock.search.mockResolvedValueOnce([{ title: 'Result', size: 100 }]);