docs(plan): add Go rewrite design task breakdown (#625)

[fengyizhu]

Summary

• add the team-oriented Go rewrite planning document under docs/design/go-rewrite-architecture-plan.md
• break the planning work into concrete design tracks with outputs, dependencies, and suggested roles
• include validation questions for each task so the team can judge whether a design topic is actually clear before moving on

Test plan

• Verify the document is present at docs/design/go-rewrite-architecture-plan.md
• Confirm the content focuses on task breakdown rather than background-only discussion
• Confirm the plan is associated with issue 跟踪 Go 版本完整重构 #625

Relates to #625

🤖 Generated with Claude Code