Resizable left sidebar

[msabramo]

Fixes https://github.com/modelcontextprotocol/inspector/issues/457

Vibe-coded with Cursor

Motivation and Context

Make left sidebar resizable so long URLs can be viewed in their entirety.

Before

Sidebar narrow so can't see full URL

After

Sidebar can be expanded to see full URL

How Has This Been Tested?

npm run dev

and then resize in browser

Breaking Changes

No

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [X] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Documentation update

Checklist

• [x] I have read the MCP Documentation
• [x] My code follows the repository's style guidelines
• [x] New and existing tests pass locally
• [ ] I have added appropriate error handling
• [x] I have added or updated documentation as needed

Additional context