Plugin install tip shows for already-installed plugins

Description

The contextual tip system suggests installing plugins that are already installed. For example, when working with HTML/CSS, Claude Code displays:

Tip: Working with HTML/CSS? Install the frontend-design plugin:
    /plugin install frontend-design@claude-code-plugins

...even though frontend-design is already installed and active (visible in the available skills list).

Expected behavior

The tip system should check whether the plugin is already installed before suggesting it.

Steps to reproduce

1. Install the frontend-design@claude-code-plugins plugin
2. Work on any HTML/CSS-related task
3. Observe the tip suggesting to install the already-installed plugin

Environment

• Claude Code with frontend-design skill already installed and functional
• Model: Opus 4.6
• Platform: Linux