2.6.0

chore: bump to v2.6.0 and fix CI build + desktop auto-load

- Remove package-lock.json from .gitignore and commit lock file for reproducible CI builds
- Remove --publish always from electron-builder (redundant with separate upload step)
- Remove duplicate CSC_IDENTITY_AUTO_DISCOVERY env var in release.yml
- Add Linux build dependencies (libfuse2, libxkbcommon0) for AppImage
- Fix electron-adapter.js ReferenceError: undefined autoLoadBalatroFiles
- Bump version to 2.6.0 in package.json, index.html, translations.js (EN/ES/ZH)
- Add .DS_Store and .claude/ to .gitignore

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