[Bug] Slash command autocomplete excludes plugin skills

Bug Description
Title: Slash command autocomplete doesn't include plugin skills

Description:

When I type / in Claude Code, the autocomplete menu doesn't show skills from installed plugins. I have to know the exact skill name (e.g., /interview) and type it manually.

Expected behavior:

• Type / → see all available skills including plugin skills
• Type /int → autocomplete suggests /interview from my plugin
• Plugin skills appear alongside built-in commands

Actual behavior:

• Only built-in commands appear in autocomplete
• Plugin skills work if typed exactly (e.g., /interview loads the skill)
• No discoverability for plugin skills

Impact:

• Users don't know what skills are available from plugins
• README documentation says "invoke with /skill-name" but users can't discover skill names
• Reduces plugin usefulness since skills are hidden

Environment:

• Claude Code CLI (latest)
• Plugin: ajbm-dev@ajbm with 6 skills installed
• Skills work when invoked directly, just not discoverable

Environment Info

• Platform: darwin
• Terminal: WarpTerminal
• Version: 2.1.4
• Feedback ID: e962c338-eb65-4f1f-ae82-42d1ed2f1cdf