docs: add MCP service guide and update README

[RerankerGuo]

Summary

This PR addresses #357 by adding comprehensive MCP service documentation and updating the README.

Changes

New File: docs/en/mcp_service.md

A complete MCP service guide covering:

• Overview: Transport types (stdio, SSE, streamable-http) and architecture
• Quick Start: Commands to start MCP service with each transport
• Configuration: YAML examples for transport selection, injected parameters
• Tool Reference: Complete tables for all MCP-exposed tools organized by category:
  • File Operations (write, read, edit, delete, move, list, stat, frontmatter)
  • Search and Retrieval (search, node_search, traverse)
  • Memory Management (auto_memory, auto_resource, auto_dream, proactive, daily_list)
  • Indexing (reindex, bm25_search, vector_search)
• Agent Integration: Setup guides for Claude Code, Codex, and generic MCP clients
• Response Format: Explanation of string-based answer format for LLM consumers
• Troubleshooting: Common issues and solutions

Modified: README.md

• Added link to the new MCP Service Guide in the Agent Integration section

Rationale

The MCP service is a core integration path for ReMe (as highlighted in the README and existing plugin infrastructure). A dedicated, comprehensive guide helps:

• New users understand how to expose ReMe as an MCP service
• Agent developers integrate ReMe memory into their frameworks
• Document the complete tool surface available to MCP consumers

Testing

• Documentation-only change, no code modifications
• Verified all tool names and parameters match current implementation
• Verified configuration keys match reme/config/default.yaml
• Cross-referenced existing plugin documentation

Checklist

• Documentation follows existing style and structure
• All tool names and parameters match current codebase
• Configuration examples use valid YAML syntax
• Cross-references to existing documentation are correct
• README link was added in the appropriate section

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

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