Plugin marketplace cache not updated before install/update

Bug

When using self-hosted plugin marketplaces, the local marketplace cache is never updated (git fetch) before:

• Installing a plugin (claude plugin install)
• Updating a plugin (clicking "Update" in the UI)

This causes users to install outdated versions even when newer versions exist on GitHub.

Steps to Reproduce

1. Add a self-hosted marketplace: claude plugin marketplace add github:user/repo
2. Install a plugin from it: claude plugin install myplugin@mymarketplace
3. Push a new version to GitHub (update plugin.json version)
4. Try to update: Click "Update" button or run claude plugin install again
5. Result: Old version is installed, new version is ignored

Expected Behavior

The plugin manager should git fetch the marketplace repo before comparing/installing versions.

Actual Behavior

The plugin manager uses the stale local cache in ~/.claude/plugins/marketplaces/<name>/ without fetching updates from the remote.

Workaround

Manually update the marketplace cache:

cd ~/.claude/plugins/marketplaces/<marketplace-name>
git pull origin main

Then reinstall the plugin.

Environment

• Claude Code version: Latest
• OS: macOS