Add TopicGate MCP Server APIs And Middleware

[Dumdart]

Summary

Add a structured MCP server layer for TopicGate, exposing broker, connection, dashboard, preview, publish, subscription, and topic APIs with shared models and middleware.

Changes

Features

• Add MCP server initialization and API endpoints for TopicGate workflows.
• Add dashboard preview support and GUI integration.
• Document MCP usage and update project configuration and dependencies.

Refactoring

• Introduce shared MCP models and package structure.
• Add centralized error-handling and logging middleware.

Improvements

• Expand automated coverage for MCP APIs, dashboard behavior, and middleware.
• Update lockfile and ignore rules.

Testing

• Added and updated tests covering MCP APIs, dashboard functionality, and middleware behavior.