fix(synology): use Thumbnail API with size xl for originals to avoid HEIC

Replace SYNO.Foto.Download with SYNO.Foto.Thumbnail (size=xl) for the
original kind, mirroring the Immich approach. Synology's download endpoint
returns the raw file (HEIC for iPhone photos), while the Thumbnail API
always serves a browser-compatible JPEG render.

server/tests/integration/memories-synology.test.ts

@@ -166,16 +166,6 @@ vi.mock('../../src/utils/ssrfGuard', async () => {
       });
     }
 
-    // Original download
-    if (apiName === 'SYNO.Foto.Download') {
-      const imageBytes = Buffer.from('fake-synology-original');
-      return Promise.resolve({
-        ok: true, status: 200,
-        headers: { get: (h: string) => h === 'content-type' ? 'image/jpeg' : null },
-        body: new ReadableStream({ start(c) { c.enqueue(imageBytes); c.close(); } }),
-      });
-    }
-
     return Promise.reject(new Error(`Unexpected safeFetch call to Synology: ${u}, api=${apiName}`));
   }