Summary

Add a "Test Connection" button to tool connection dialogs to validate provider credentials before saving. Supports all tool types (MCP, API, etc.).

Problem / Opportunity

Users currently have no way to verify their tool provider credentials are correct before saving the connection, leading to failed connections and confusion.

Proposal

Add a test connection feature that validates credentials by attempting to connect to the tool provider and verifying the connection works. The backend routes to appropriate test logic based on tool type (MCP fully implemented, API tools can be added later).

Acceptance Criteria

• "Test Connection" button appears in tool connection dialogs
• Button validates credentials and displays success/error message
• Connection test is required before saving in create mode
• Works for MCP tool types (notion, github, custom, etc.)
• Backend architecture supports extension to other tool types (API, etc.)