Develop tuig

The only runtime is Rust/Ratatui in native/agent-terminal-ui. Python is used for repository validation and native PTY tests, not as a frontend.

Read AGENTS.md and the owning requirement in specs/terminal-runtime before editing. Keep Arbora responsible for authorization, task lifecycle and served operations. Do not add a local model, tool executor or compatibility frontend.

Run Cargo format, test and Clippy checks with the locked manifest. Run the Python native PTY harness against the same compiled executable through TUI_NATIVE_TEST_BINARY. Record focused results separately from live-service, full parity and release qualification. Do not publish without authorization.