Add comprehensive validation and normalization for MCP server configurations
to ensure consistent and properly formatted server definitions. This includes:

- New error code for invalid MCP server configurations
- Utilities to validate server config structure and values
- Normalization of different input formats to a consistent output format
- Support for both Claude Code wrapper format and direct server definitions
- Proper validation of transport types (http, stdio), URLs, headers, and environment variables

The service layer has been updated to use these utilities to ensure all
persisted server configurations are valid and properly formatted.