feat: show skills in status and sidebar

[connorads]

Adds skills list to the status page and sidebar. Fixes #7533

Previously, I believe there was no way to see which skills were loaded in a session. Users had to explicitly ask the agent about loaded skills and hope for an accurate response.

Demos

Multiple skills

Shown in status and sidebar

Single skill

Doesn't show as collapsible sidebar ▶︎

No skills

Implementation considerations

I'm not precious about any of this just thought I'd mention it in case people want to change it.

• Uses green dot indicator (matching MCP) to show skills are active
  • Note: Currently I believe there's no deactivated state for skills, but the indicator maintains visual consistency with MCP and leaves room for future state management
• Skills are ordered alphabetically in the sidebar (same as MCP servers)
• When collapsed, the Skills section doesn't show a count (unlike MCP's "4 active")
  • Rationale: Skills don't have active/inactive states like MCP servers, so showing a count felt unnecessary. Skills are either loaded or not shown at all. And all the other sections don't have a count.
• Location/source information is not displayed
  • Consistent with MCP servers which I believe also don't show their source in status or sidebar

[connorads]

Previously, I believe there was no way to see which skills were loaded in a session. Users had to explicitly ask the agent about loaded skills and hope for an accurate response.

I've since learned that you can run opencode debug skill
But it'd still be nice to have something in the TUI (and more in the web/desktop view in the future)

➜ opencode debug skill
[
  {
    "name": "frontend-design",
    "description": "Create distinctive, production-grade frontend interfaces with high design quality. Use this skill when the user asks to build web components, pages, or applications. Generates creative, polished code that avoids generic AI aesthetics.",
    "location": "/Users/connor.adams/.config/opencode/skill/frontend-design/SKILL.md"
  },
  {
    "name": "homebrew-cask-authoring",
    "description": "Create, update, validate, and submit Homebrew Casks. Use when the user mentions Homebrew cask/cask, Homebrew/homebrew-cask, adding a new cask, updating a cask, cask token naming, sha256, url verified:, livecheck, zap/uninstall, or when asked to run brew style/audit for a cask.",
    "location": "/Users/connor.adams/.config/opencode/skill/homebrew-cask-authoring/SKILL.md"
  }
]

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[connorads]

If/when #7527 is merged I can also manually retest this PR before merging