[FEATURE]: Add .claude/commands/ compatibility (like .claude/skills/)

[SeanZoR]

Summary

OpenCode supports Claude Code's .claude/skills/ paths for skill discovery, but doesn't support .claude/commands/ paths for command discovery. This creates an inconsistent migration experience for users coming from Claude Code.

Current Behavior

Skills - OpenCode searches these paths (per docs):

• .opencode/skill/<name>/SKILL.md (project)
• ~/.config/opencode/skill/<name>/SKILL.md (global)
• .claude/skills/<name>/SKILL.md (project, Claude-compatible)
• ~/.claude/skills/<name>/SKILL.md (global, Claude-compatible)

Commands - OpenCode only searches (per docs):

• .opencode/command/ (project)
• ~/.config/opencode/command/ (global)

No .claude/commands/ compatibility.

Proposed Behavior

Add Claude-compatible command paths to match the skills behavior:

• .claude/commands/<name>.md (project)
• ~/.claude/commands/<name>.md (global)

Use Case

Users migrating from Claude Code who have existing commands at ~/.claude/commands/ currently need to either:

1. Copy/move files to ~/.config/opencode/command/
2. Create symlinks manually

This is friction that doesn't exist for skills.

Related Issues

• #6266 - .claude/skills/ compatibility discussion
• #6177 - Skill discovery paths
• #6252 - PR that added project-level .claude/skills/ support