feat(opencode): Add commandsPath support for OpenCode client

[christso]

Summary

The documentation states that OpenCode supports commands at .opencode/commands/, but the code doesn't implement this.

Current State

Documentation (after this PR's fixes):

• docs/src/content/docs/reference/clients.mdx: Lists OpenCode with .opencode/commands/
• README.md: Shows OpenCode with .opencode/commands/ in the client comparison table

Code:

• src/models/client-mapping.ts: OpenCode client mapping has no commandsPath property
• Commands are only synced when commandsPath exists (see copyCommands in src/core/transform.ts)

Expected Behavior

When plugins have a commands/ directory and OpenCode is in the workspace's clients list, commands should be synced to .opencode/commands/.

Implementation

Add commandsPath to the OpenCode client mapping:

```typescript
opencode: {
commandsPath: '.opencode/commands/', // Add this line
skillsPath: '.agents/skills/',
agentFile: 'AGENTS.md',
},
```

References

• OpenCode commands docs: https://opencode.ai/docs/commands/
• Per-project commands location: .opencode/commands/