Add slash-command autocomplete to the Netclaw TUI

[Aaronontheweb]

Outcome

A user can discover and select an invocable skill in Netclaw chat.

Requirements

• Detect a leading slash command.
• Query the daemon completion API.
• Show only skills which the caller can use.
• Show argument hints.
• Support keyboard selection and cancellation.
• Preserve current slash dispatch behavior.
• Show an explicit error when the catalog request fails.
• Add headless typed-key coverage.
• Add native smoke tapes.

Dependency

This issue depends on the skill catalog HTTP API.