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/main/download-manager.ts

@@ -5231,6 +5231,7 @@ export class DownloadManager extends EventEmitter {
         // Unrestrict succeeded - reset provider failure counter
         this.recordProviderSuccess(this.getProviderFailureKeyForItem(item, unrestricted.provider));
         item.provider = unrestricted.provider;
+        item.providerLabel = unrestricted.providerLabel;
         item.retries += unrestricted.retriesUsed;
         item.fileName = sanitizeFilename(unrestricted.fileName || filenameFromUrl(item.url));
         try {