Fix core download bugs: resume corruption, 416 handling, stream leak, drain timeout

- HTTP 200 on resume: detect server ignoring Range header, write in truncate mode
  instead of appending (prevents doubled/corrupted files)
- HTTP 416 without Content-Range: assume complete if >1MB exists instead of
  deleting potentially multi-GB finished files
- Stream handle leak: explicit destroy() after finally to prevent fd exhaustion
- Drain timeout: don't abort controller on disk backpressure, let inner retry
  loop handle it instead of escalating to full stall pipeline

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "real-debrid-downloader",
-  "version": "1.4.88",
+  "version": "1.4.89",
   "description": "Real-Debrid Downloader Desktop (Electron + React + TypeScript)",
   "main": "build/main/main/main.js",
   "author": "Sucukdeluxe",