add marketplace config

[arre-ankit]

Migrated from individual plugin.json to a centralized marketplace.json approach for distributing Cloudflare Skills via Claude Code's plugin marketplace system.

What Changed

• Removed: Individual plugin.json files
• Added: .claude-plugin/marketplace.json as the single source of truth for plugin distribution

Why This Change?

According to the Claude Code Plugin Marketplaces documentation, GitHub-hosted marketplaces are the recommended distribution method for Claude Code plugins.

When using the marketplace approach:

1. Simplified Structure: A marketplace.json file can define all plugin metadata inline, eliminating the need for separate plugin.json files in each skill directory.

2. Easier Distribution: Users can install the entire skill collection with:

   /plugin marketplace add cloudflare/skills
   

3. Better Discovery: All available skills are catalogued in one place, making it easier for users to browse and install.

How Users Install

After this change, users can add the marketplace and install skills:

# Add the marketplace
/plugin marketplace add cloudflare/skills

[arre-ankit]

@whoiskatrin happy new year, if you're back please take a look.

[elithrar]

I've updated this in #3 since there are multiple new skills. Thanks for the push!