feat: embed a no-GUI CLI runtime mode

[openai0229]

Summary

• make the Rust CLI attach to an existing local host or automatically start the shared RuntimeHost without Tauri, WebKit, or HTTP
• add explicit attach and foreground runtime modes with active-work-aware idle shutdown
• share packaged runtime resource resolution across Desktop, Web, and CLI hosts
• embed the matching CLI binary in macOS, Windows, and Linux desktop packages

Verification

• cargo test --workspace --all-targets --locked: 857 passed, 10 ignored
• strict workspace Clippy passes on Rust 1.95 and 1.98
• Rust 1.88 all-target compatibility checks pass
• release smoke: health ready, Java dormant, approximately 12.2 MB RSS
• automatic headless host lifecycle integration test
• package shell syntax and macOS embedded-CLI verification checks