[FEATURE]: Support commands in .agents/commands

[Arcadi4]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Add command discovery for .agents/commands/**/*.md, matching the existing .agents/skills convention.

opencode already discovers reusable skills from .agents/skills, but slash command markdown is only discovered from .opencode/command(s). This makes it harder to keep agent-related commands and skills together in shared dotfile/project setups.

This is related to #14240, but intentionally narrower: support the .agents/commands convention without adding a general configurable path system.

[github-actions]

Thanks for updating the issue! It now meets our contributing guidelines. We'll take a look.

[mugnimaestra]

I have opened #30629 which implements this by adding command discovery from .agents/commands/ and .claude/commands/ (mirroring the existing skill discovery paths), plus a commands.paths config field for custom folders. Would appreciate feedback on the approach.