feat: add memory_search and memory_timeline tools

[yczc3999]

Summary

• add a new MCP service module that exposes memory_search, memory_list, and memory_stats handlers using existing memory APIs
• initialize the MCP server during plugin startup and add new OpenCode plugin tools memory_search and memory_timeline for richer memory access
• update package metadata for MCP discovery and add @modelcontextprotocol/sdk dependency

Validation

• bun run typecheck
• bun run build

[tickernelz]

all your PRs is it already tested in your local? all working fines?