plugins-index.json can drift out of sync with actual plugin directories

[StencilwashCoder]

The plugins-index.json file serves as the registry for all available plugins, but there's no automated check that every plugin listed in the index actually has a corresponding directory in plugins/.

As plugins are added, renamed, or removed, the index can drift out of sync with the filesystem. This leads to:

• Broken links in the marketplace
• Users trying to install plugins that don't exist
• The plugin finder referencing missing skills

A simple CI check or pre-commit hook that verifies every entry in plugins-index.json has a matching plugins/<name>/ directory would prevent this. Conversely, it should also check that every plugin directory is listed in the index.