fix: resolve additional bugs identified in code review

- core: remove DispatchGroup from MediaExtractionEngine to fix hanging on yt-dlp launch failure
- core: clear readabilityHandlers in Aria2DownloadEngine if process fails to launch
- core: fix TOCTOU type warning for findFreePort
- build: fix inverted logic in Mach-O validation script
- ci: fix hardcoded macOS SDK version check in release workflow
- ci: prevent workflow_dispatch from failing on verify-tag

Scripts/create_app_bundle.sh

@@ -20,7 +20,7 @@ cd "$ROOT_DIR"
 is_valid_mach_o() {
   local path="$1"
   if ! file "$path" | grep -q 'Mach-O'; then
-    return 0
+    return 1
   fi
 
   lipo -archs "$path" >/dev/null 2>&1