feat: Plugin README viewer

[bojanrajkovic]

Summary

Show the plugin's README in a scrollable pane for more detailed information.

Motivation

Plugin descriptions are often brief. The full README contains installation instructions, usage examples, configuration options, and other valuable information.

Proposed Implementation

• Add ? or Enter key to open README viewer for selected plugin
• Show README in a full-screen or modal view with scrolling
• Parse and render Markdown (or show plain text)
• Add q or Esc to close and return to main view

Technical Notes

• README location: <plugin_path>/README.md
• May need a Markdown renderer (glamour or similar)
• For uninstalled plugins, may need to fetch from marketplace/GitHub

Complexity

Medium - Need Markdown rendering and new view mode.