chore: bump version to 3.9.0-beta.1
- Update version in package.json, Cargo.toml, tauri.conf.json
- Add CHANGELOG entry for v3.9.0-beta.1 with:
- Local Proxy Server feature
- Auto Failover with circuit breaker
- Skills multi-app support
- Provider icon colors
- 25+ bug fixes
- Add proxy feature guide documentation (Chinese)
Jason