plugin install should support --force flag to clean cached plugin before reinstall

Is your feature request related to a problem?

When reinstalling a Claude Code plugin, the cached version at ~/.claude/plugins/cache/ persists. This causes stale artifacts (old .venv, outdated config, leftover MCP server registrations) to remain, leading to hard-to-debug issues like MCP servers connecting to wrong endpoints or using outdated dependencies.

Currently the only workaround is manually deleting the cache directory before reinstalling:

rm -rf ~/.claude/plugins/cache/<plugin-name>/
claude plugin install <plugin>

Describe the solution you'd like

Add a --force (or --clean) flag to claude plugin install:

claude plugin install --force <plugin>

This should:

1. Remove the existing cached plugin directory before installation
2. Perform a fresh install as if the plugin was never installed

Alternatives considered

• Documenting the manual rm -rf workaround — fragile, users need to know the cache path
• Adding a separate claude plugin clean <plugin> command — viable but adds another command to remember

Additional context

Current plugin install options only support -s, --scope <scope> — no cache management flags exist.