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/app/requests.page.test.tsx

@@ -33,6 +33,10 @@ vi.mock('@/components/requests/RequestCard', () => ({
   ),
 }));
 
+vi.mock('@/contexts/PreferencesContext', () => ({
+  usePreferences: () => ({ squareCovers: false, setSquareCovers: vi.fn(), cardSize: 5, setCardSize: vi.fn() }),
+}));
+
 describe('RequestsPage', () => {
   beforeEach(() => {
     resetMockAuthState();