Detect hoster error-page downloads (<512 B) and trigger retry

Some hosters return tiny error responses (e.g. 9 bytes) with HTTP 200.
- downloadToFile: detect files <512 B, log content, delete and throw for retry
- Post-download: catch <512 B files even when totalBytes is unknown
- Logs the error-page content for debugging

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "real-debrid-downloader",
-  "version": "1.4.81",
+  "version": "1.4.82",
   "description": "Real-Debrid Downloader Desktop (Electron + React + TypeScript)",
   "main": "build/main/main/main.js",
   "author": "Sucukdeluxe",