Set retention-days: 30 on all upload-artifact steps

Reduce artifact retention from default 90 days to 30 days.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: synle

.github/workflows/build.yml

@@ -102,6 +102,7 @@ jobs:
             src-tauri/target/${{ matrix.target }}/release/bundle/deb/*.deb
             src-tauri/target/${{ matrix.target }}/release/bundle/appimage/*.AppImage
             src-tauri/target/${{ matrix.target }}/release/bundle/rpm/*.rpm
+          retention-days: 30
           compression-level: 9
           if-no-files-found: ignore