♻️ refactor(bestdebrid): switch from browser login to cookie file import

Replace BrowserWindow-based login flow with Netscape cookie file import
for BestDebrid authentication. Cloudflare Turnstile captcha cannot be
solved in Electron's embedded browser, so users export cookies from
their real browser and import them here.

- Rewrite bestdebrid-web.ts: remove BrowserWindow/CDP code, add
  parseNetscapeCookieFile() and importCookiesFromFile()
- Add file picker dialog for .txt cookie files in main IPC handler
- Update IPC channel from OPEN_BESTDEBRID_LOGIN to IMPORT_BESTDEBRID_COOKIES
- Update preload bridge and renderer UI with cookie import button
- Fix pLabel scope in downloadToFile (pass as parameter from processItem)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/preload/preload.ts

@@ -54,7 +54,7 @@ const api: ElectronApi = {
   openSessionLog: (): Promise<void> => ipcRenderer.invoke(IPC_CHANNELS.OPEN_SESSION_LOG),
   openRealDebridLogin: (): Promise<void> => ipcRenderer.invoke(IPC_CHANNELS.OPEN_REALDEBRID_LOGIN),
   openAllDebridLogin: (): Promise<void> => ipcRenderer.invoke(IPC_CHANNELS.OPEN_ALLDEBRID_LOGIN),
-  openBestDebridLogin: (): Promise<void> => ipcRenderer.invoke(IPC_CHANNELS.OPEN_BESTDEBRID_LOGIN),
+  importBestDebridCookies: (): Promise<number> => ipcRenderer.invoke(IPC_CHANNELS.IMPORT_BESTDEBRID_COOKIES),
   getAllDebridHostInfo: (): Promise<AllDebridHostInfo> => ipcRenderer.invoke(IPC_CHANNELS.GET_ALLDEBRID_HOST_INFO),
   retryExtraction: (packageId: string): Promise<void> => ipcRenderer.invoke(IPC_CHANNELS.RETRY_EXTRACTION, packageId),
   extractNow: (packageId: string): Promise<void> => ipcRenderer.invoke(IPC_CHANNELS.EXTRACT_NOW, packageId),