Plugin install says 'already installed' when plugin is only installed for a different project

Bug Description

When running /plugin install frontend-design@claude-plugins-official, the CLI responds with:

Plugin 'frontend-design@claude-plugins-official' is already installed. Use '/plugin' to manage existing plugins.

However, the plugin is only installed with local scope for a different project path. It is not active or available in the current project.

Expected Behavior

The install command should detect that the plugin isn't installed for the current project and either:

1. Offer to install it for the current project (with scope selection)
2. Inform the user it's installed elsewhere and prompt to add it here

Actual Behavior

The command treats the plugin as globally installed and refuses to install it, with no option to add it to the current project.

Steps to Reproduce

1. Install a plugin with local scope in project A
2. Open Claude Code in project B (different directory)
3. Run /plugin install <same-plugin>
4. Observe: "already installed" message, even though it's not available in project B

Environment

• Claude Code CLI (latest as of 2026-02-08)
• Linux (Ubuntu-based)

Workaround

Manually edit ~/.claude/plugins/installed_plugins.json to add a second entry for the plugin scoped to the current project.