Support native .skill zip file format in plugin auto-discovery

Feature Request

Claude Code's plugin system currently only discovers skills in the extracted directory format (skills/<name>/SKILL.md), but does not support the packaged .skill zip format that Claude.ai (web/desktop) handles natively.

Problem

The .skill file format is an Anthropic-created packaging format (a zip archive containing SKILL.md and references/ directories). Users who create or download .skill files for use in Claude.ai must manually extract them into the correct directory structure for Claude Code to discover them. This creates an unnecessary friction point and a parity gap between the two products.

Expected Behavior

Placing .skill files in ~/.claude/plugins/<plugin>/skills/ (or a project-level equivalent) should work the same as having the extracted directory — Claude Code should auto-discover and load skills from .skill zip archives, just as Claude.ai does.

Current Workaround

Manually unzip each .skill file into the skills/ directory:

cd ~/.claude/plugins/my-plugin/skills
unzip my-skill.skill
rm my-skill.skill

Context

• The .skill format bundles a SKILL.md and optional references/ directory into a single zip
• Claude.ai supports this format natively
• Claude Code requires the extracted directory structure
• This creates a confusing experience for users who work across both interfaces