fix(media): reject extension cookie headers for media

Keep explicit media requests on yt-dlp's configured browser-cookie path and preserve cookies for normal captures.

src/store/useDownloadStore.test.ts

@@ -818,6 +818,7 @@ describe('useDownloadStore', () => {
     expect(state.isAddModalOpen).toBe(true);
     expect(state.pendingAddUrls).toBe('https://adult.example/watch/123');
     expect(state.pendingAddMediaUrls).toEqual(['https://adult.example/watch/123']);
+    expect(state.pendingAddCookies).toBe('');
   });
 
   it('deduplicates forced media URLs and drops stale media intent when opening fresh', async () => {

src/store/useDownloadStore.ts

@@ -552,12 +552,17 @@ export const useDownloadStore = create<DownloadState>((set, get) => ({
     const urls = [...new Set(request.urls.map(url => url.trim()).filter(Boolean))];
     if (urls.length === 0) return;
 
+    // Explicit media uses yt-dlp and its configured browser-cookie source.
+    // Passing Firefox's complete page Cookie header can exceed YouTube's
+    // request-header limit; ordinary captured file downloads keep it.
+    const cookies = request.media === true ? null : request.cookies;
+
     get().openAddModalWithUrls(
       urls.join('\n'),
       request.referer,
       urls.length === 1 ? request.filename : null,
       request.headers,
-      request.cookies,
+      cookies,
       request.media === true
     );
   },