⚡️ perf: improve extraction status, stuck detection, and retry logic

- Extraction status: "Entpackt - Done" / "Entpacken - Ausstehend"
- Per-item extraction progress (no cross-contamination)
- Validating-stuck watchdog: abort items stuck >45s in "Link wird umgewandelt"
- Global stall timeout reduced 90s → 60s, unrestrict timeout 120s → 60s
- Unrestrict retry: longer backoff (5/10/15s), reset partial downloads
- Stall retry: reset partial downloads for fresh link
- Mega-Web generate: max 30 polls (was 60), 45s overall timeout
- Mega-Web session refresh: 10min (was 20min)
- Comprehensive logging on all retry/failure paths

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "real-debrid-downloader",
-  "version": "1.4.73",
+  "version": "1.4.74",
   "description": "Real-Debrid Downloader Desktop (Electron + React + TypeScript)",
   "main": "build/main/main/main.js",
   "author": "Sucukdeluxe",