[Feature] Add optional ACP coding-agent package

[scald]

What problem are you trying to solve?

NOOA retains a capable InteractiveAgent, CodeAct runtime, repository tools, and host-facing events, but it has no working terminal client. PR #9 removed the previous TUI because the public commands referenced an unpublished external package and failed at runtime. Users currently need to build a custom host to use NOOA as an interactive coding agent.

No existing issue or PR mentions ACP or the Agent Client Protocol. PR #62 added external nooa_cli.commands entry points and used tui as its motivating example, which provides the extension point this proposal needs.

Proposed solution

Add an optional nooa-acp workspace distribution that:

• hosts a CodingInteractiveAgent over the open Agent Client Protocol on stdio;
• maps NOOA messages, tool lifecycle, usage, and cancellation events to ACP updates;
• registers nooa acp through the entry-point mechanism added in feat(cli): let external packages add nooa subcommands via entry points #62;
• keeps ACP dependencies out of core nooa and the default nooa-cli;
• interoperates with separately installed ACP clients without importing or redistributing them;
• includes deterministic protocol tests and documentation for LiteLLM-supported models.

The initial implementation supports one session per process, text prompts, resource links, stdio MCP servers, Markdown responses, CodeAct tool progress, usage, cancellation, and clean shutdown.

Alternatives considered

• Restore a native in-repo TUI: duplicates the client interface, expands UI dependencies, and revisits the surface removed in Chore/strip tui #9.
• Bundle a client implementation: increases dependency and release coupling instead of using the protocol boundary.
• Use another coding agent as the backend: its agent loop would replace NOOA CodeAct, context, tools, and retries rather than expose NOOA itself.
• Publish from a separate repository: increases release/version skew with the NOOA event and InteractiveAgent APIs.

Additional context

The ACP Python SDK is Apache-2.0. The implementation uses SDK 0.11 because 0.12 is inside the repository's seven-day dependency quarantine. Generated code and shell execution remain subject to NOOA's existing sandbox warning; the working-directory boundary is not presented as containment.