feat: add MCP server for AI assistant integration

[sanggggg]

Summary

Add retrochat-mcp crate that exposes chat session query and analytics capabilities via Model Context Protocol (MCP). This enables AI assistants like Claude and Cursor to query and analyze chat history.

Features

• Read-only MCP server with stdio transport
• 4 MCP tools:
  • list_sessions - Query and filter chat sessions with pagination
  • get_session_detail - Get full session details with all messages
  • search_messages - Full-text search across all messages
  • get_session_analytics - Get analytics for a session
• Comprehensive error handling and validation (UUID, dates)
• Pretty-printed JSON responses for easy AI consumption
• Unit tests for all components (9 tests passing)
• Documentation in CLAUDE.md with configuration examples

Technical Details

• Uses rmcp 0.11 with server, macros, and transport-io features
• Shares database with CLI/TUI (read-only access)
• Logs to stderr to avoid interfering with stdio transport
• Supports RUST_LOG environment variable for log level control

Usage

# Run MCP server
cargo mcp

# Run tests
cargo tmcp

# With debug logging
RUST_LOG=debug cargo mcp

Configuration

Claude Desktop (~/Library/Application Support/Claude/claude_desktop_config.json):

{
  "mcpServers": {
    "retrochat": {
      "command": "/path/to/retrochat-mcp",
      "args": []
    }
  }
}

Cursor (.cursor/mcp.json):

{
  "mcpServers": {
    "retrochat": {
      "command": "cargo",
      "args": ["run", "-p", "retrochat-mcp"],
      "cwd": "/path/to/retrochat"
    }
  }
}

Testing

• All unit tests passing (9/9)
• Clippy clean with -D warnings
• Release build successful
• Formatted with cargo fmt

Files Changed

• Added crates/retrochat-mcp/ crate (5 files, 813 lines)
• Updated workspace Cargo.toml with new member and dependencies
• Updated .cargo/config.toml with mcp and tmcp aliases
• Updated CLAUDE.md with comprehensive MCP server documentation