[WIP] feat: add ACP support

[stay-foolish-forever]

Description

Add Agent Client Protocol (ACP) support to the H2 2026 roadmap.

This draft PR serves as a planning placeholder while the implementation approach is evaluated. The current direction is to expose OpenCodeReview as a specialized review agent for Paseo and other ACP-compatible clients through a decoupled ACP server adapter.

This PR does not implement ACP support yet.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactoring (no functional changes)
• Documentation update
• CI / Build / Tooling

How Has This Been Tested?

Documentation-only change; verified with git diff --check.

• make test passes locally
• Manual testing (describe below)

Checklist

• My code follows the project's coding style (go fmt, go vet)
• I have performed a self-review of my code
• I have added tests that prove my fix is effective or my feature works
• New and existing unit tests pass locally with my changes
• I have updated the documentation accordingly (if applicable)
• I have signed the CLA

Related Issues

Tracks #674.

[github-actions]

✅ OpenCodeReview: No supported files changed.