ci(desktop): bump upload-artifact v5 -> v7 (node24)

upload-artifact@v5 still targets node20; v6+ moved to node24. v7 is the
latest. This clears the last remaining Node.js 20 deprecation warning.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/desktop-release-package.yml

@@ -176,7 +176,7 @@ jobs:
           Get-ChildItem artifacts/windows/out | Format-Table Name, Length
 
       - name: Upload workflow artifact
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v7
         with:
           name: GenericAgent-Desktop-Windows-Portable-${{ github.run_number }}
           path: |
@@ -388,7 +388,7 @@ jobs:
           ls -lh artifacts/linux/out
 
       - name: Upload workflow artifact
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v7
         with:
           name: GenericAgent-Desktop-Linux-Portable-${{ github.run_number }}
           path: |
@@ -653,7 +653,7 @@ jobs:
           find "$DMG_STAGE" -maxdepth 2 -print | sort
 
       - name: Upload workflow artifact
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v7
         with:
           name: GenericAgent-Desktop-macOS-DMG-${{ github.run_number }}
           path: artifacts/macos/out/*