fix: Correct marketplace name from claude-code-marketplace to claude-code-plugins

The plugin-dev README incorrectly referenced the marketplace as "claude-code-marketplace"
when it should be "claude-code-plugins" as defined in .claude-plugin/marketplace.json.

This corrects the installation instructions and contributing section to use the
proper marketplace name, ensuring users can correctly install the plugin.

Related to the tips feature issue where plugins were not being detected as installed
due to incorrect marketplace name references.

plugins/plugin-dev/README.md

@@ -195,10 +195,10 @@ Use this workflow for structured, high-quality plugin development from concept t
 
 ## Installation
 
-Install from claude-code-marketplace:
+Install from claude-code-plugins:
 
 ```bash
-/plugin install plugin-dev@claude-code-marketplace
+/plugin install plugin-dev@claude-code-plugins
 ```
 
 Or for development, use directly:
@@ -378,7 +378,7 @@ All skills emphasize:
 
 ## Contributing
 
-This plugin is part of the claude-code-marketplace. To contribute improvements:
+This plugin is part of the claude-code-plugins. To contribute improvements:
 
 1. Fork the marketplace repository
 2. Make changes to plugin-dev/