feat: add MCP server for AI-powered member management

This change implements a Model Context Protocol (MCP) server that
enables AI assistants to manage society members through natural
language interactions.

Changes:
- Add MCP server implementation (src/mcp_server.py)
- Implement 4 core tools:
  * list_members - Query all members
  * get_member - Get specific member by ID
  * create_member - Create new member
  * update_member - Update member information
- Add mcp and httpx dependencies to pyproject.toml
- Update README with comprehensive MCP server documentation
- Create OpenSpec proposal in openspec/changes/add-mcp-server/

The MCP server connects to the GraphQL API via HTTP and provides
structured tools that abstract away GraphQL complexity.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

pyproject.toml

@@ -11,6 +11,8 @@ dependencies = [
     "aiosqlite>=0.21.0",
     "alembic>=1.17.2",
     "fastapi>=0.121.3",
+    "httpx>=0.28.1",
+    "mcp>=1.3.2",
     "pydantic-settings>=2.12.0",
     "sqlalchemy[asyncio]>=2.0.44",
     "strawberry-graphql[fastapi]>=0.286.0",