Add a toast on connection error

[howardjohn]

Motivation and Context

When failing to connect to an MCP server, its very hard to understand why. There is only an opaque "Connection Error" message with no additional info. This also doesn't change at all on repeated attempts, so there is no indication we attempted again and failed.

This change introduces a toast to visualize the error, and adds the cause into the error message for further debugging

How Has This Been Tested?

Manually tested

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
• [x] I have added appropriate error handling
• [x] I have added or updated documentation as needed

Additional context