Feature request: expose skill invocations in the statusline API

Problem

The statusline (HUD) currently tracks low-level tool calls (Edit, Read, Grep, Bash, etc.) via display.showTools. This is useful for seeing what Claude is doing mechanically, but it doesn't surface the higher-level intent: which skills (slash commands) were invoked during a session.

For users with many custom skills configured, knowing "which skills were used" is far more informative than "which tools were called." A skill like /investigate-report or /manage-pr conveys intent and workflow stage at a glance, while a stream of Edit/Read/Grep calls does not.

Proposed solution

Add a new data dimension to the statusline API that tracks skill invocations, so statusline plugins (e.g. claude-hud) can display them. Something like:

• A display.showSkills config option (parallel to display.showTools)
• The statusline receives skill name and status (running/completed) alongside tool activity
• Example display: ⚡ investigate-report | ✓ manage-pr

This could coexist with or replace the tool activity line depending on user preference.

Alternatives considered

• Relying on tool activity alone: works for debugging but loses the "what workflow am I in" signal.
• Custom line workaround: users could manually set display.customLine but this is static and doesn't update automatically.

Additional context

Skills are a first-class concept in Claude Code with a dedicated invocation mechanism (/skill-name). Surfacing them in the statusline would make the HUD more useful for users who build skill-driven workflows.