feat(cli): add Baidu Comate support (trellis init --comate)

Feature Description

Add first-class Baidu Comate support to the Trellis CLI:

trellis init --comate

The integration should generate Comate project configuration under .comate/ while continuing to share Trellis specs, tasks, workflow, and workspace memory under .trellis/.

Proposed mapping

Proposed CLI usage

trellis init --comate
trellis init --codex --comate
trellis init --opencode --comate
trellis init --all
trellis update

Proposed MVP

1. Register comate in the platform registry.
2. Add the --comate init option.
3. Generate an always-active Trellis Rule under .comate/rules/.
4. Install Trellis workflow Skills under .comate/skills/.
5. Support idempotent init and update.
6. Add tests and documentation.

Lifecycle hooks, Commands, and deeper Subagent integration could be added later if Comate exposes stable public interfaces.

Questions

1. Would the maintainers accept Baidu Comate as a first-class platform?
2. Which existing platform adapter should be used as the preferred reference?
3. Should the initial PR focus on Rules and Skills, or also include Commands and Subagents?

I am willing to work on the implementation and submit a PR after the scope is confirmed.

References

• https://comate.baidu.com/zh
• https://cloud.baidu.com/doc/COMATE/s/Zm9l4agw3
• https://cloud.baidu.com/doc/COMATE/s/Nmma28iqe
• https://cloud.baidu.com/doc/COMATE/s/emsseobso

Motivation

Baidu Comate now provides the main primitives needed for a Trellis integration: project-level Rules, portable Agent Skills, Subagents, Commands, MCP, Memory, Spec Mode, and a CLI.

Its official documentation states that Skills follow the portable Agent Skills standard and can be stored in the repository. First-class support would let Comate users adopt the same Trellis workflow and project memory used across the other supported coding agents, without manually copying or translating Trellis files.

Alternatives Considered

1. Manually copy Trellis guidance into .comate/rules/*.mdr.
2. Manually install Trellis-compatible Skills into .comate/skills/.
3. Ask Comate to read .trellis/workflow.md at the start of every session.

These workarounds lack automatic setup, reliable updates, platform detection, and consistent team onboarding.