Add MCP entrypoint

[sanggggg]

Description

Add Model Context Protocol (MCP) entrypoint to enable retrochat to be used as an MCP server.

Context

MCP allows tools to be exposed to LLM applications in a standardized way, enabling better integration with various AI assistants and workflows.

Proposed Implementation

• Implement MCP server interface
• Expose retrochat's core functionality (import, analyze, retrospect) as MCP tools
• Add configuration for MCP server mode

Benefits

• Better integration with LLM applications
• Standardized tool interface
• Enhanced interoperability