Fix absolute archive paths, show provider account number in UI

- extractor: detect UnRAR "Cannot create...\..." error (archive with
  leading-backslash internal paths) and retry in flat mode (-e) which
  strips all paths and avoids the invalid double-separator on Windows
- types/download-manager: add providerLabel field to DownloadItem,
  store full label (e.g. "Debrid-Link #1") set at unrestrict time
- App: display providerLabel in Service column (falls back to generic
  provider name if label not yet set)

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

src/shared/types.ts

@@ -118,6 +118,7 @@ export interface DownloadItem {
   packageId: string;
   url: string;
   provider: DebridProvider | null;
+  providerLabel?: string;
   status: DownloadStatus;
   retries: number;
   speedBps: number;