Encrypted backup system + hide extracted items in package list

Backup redesign (JDownloader 2 style):
- AES-256-GCM encrypted .mdd format with fixed app key
- All credentials exported (no more ***-masking), works on any PC
- Includes settings, session AND history in backup
- Backward-compatible: auto-detects legacy JSON backups
- Normalize history entries on import
- Added debridLinkApiKeys, linkSnappy credentials to sensitive keys

Hide extracted items:
- New setting: hide completed/extracted items from package item list
- Items still count in progress stats (done/total), only hidden in UI
- Default: enabled
- Toggle in settings: "Entpackte Items in Paketliste ausblenden"

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

src/shared/types.ts

@@ -105,6 +105,7 @@ export interface AppSettings {
   accountListShowDetailedDebridLinkKeys: boolean;
   autoSortPackagesByProgress: boolean;
   autoSkipExtracted: boolean;
+  hideExtractedItems: boolean;
   confirmDeleteSelection: boolean;
   totalDownloadedAllTime: number;
   bandwidthSchedules: BandwidthScheduleEntry[];