fix: rewrite share.md as a command template with YAML frontmatter

[xiaolai]

Automated audit: This PR was generated by NLPM, a natural language programming linter, running via claude-code-action. Please evaluate the diff on its merits.

What's wrong

commands/share.md is formatted as README documentation — markdown headers (## Usage, ## How It Works, ## Requirements, etc.), code fences, and prose sections — rather than a command template. Every other command in the plugin uses a minimal YAML frontmatter block (name: + description:) followed by a prompt body. Because share.md has no frontmatter at all, it lacks both the name and description fields required for command registration, and Claude Code may not register it as a command.

The fix

Rewrote share.md as a proper command template following the same convention as the other seven commands:

• Added name: share and description: Share a visual explainer HTML page via Vercel and return a live URL as YAML frontmatter
• Replaced the README-style body with a concise prompt that instructs the agent to run share.sh and display the result
• Preserved the key functional detail: if no argument is provided, list available HTML files and ask the user to select one
• Preserved the public-deployment disclosure note inline in the prompt

The documentation content (script location, output format, requirements) is already described well in SKILL.md and in the script itself, so nothing of substance is lost.