Slack Activity v1.0.0

Local agent downloads for Windows, Linux, and macOS.\n\nAssets:\n- SlackActivity-windows-x64.exe: Windows tray app\n- slack-activity-agent-linux-x64: Linux x64 local agent\n- slack-activity-agent-macos-x64: macOS Intel local agent\n- slack-activity-agent-macos-arm64: macOS Apple Silicon local agent\n\nNote: macOS binaries are unsigned and may need codesigning/notarization before broad distribution.