docs:add simple system architecture part for README-EN.md & README.md

[Noblegasesgoo]

PR Title

docs(readme): simplify system architecture section to Layer Breakdown + Project Code Structure Tree only

Summary

This PR simplifies the System Architecture section in both Chinese and English README files by keeping only two high-signal sections:

• Layer Breakdown
• Project Code Structure Tree

The previously added overall architecture diagram and related agent-intro block were removed to keep the documentation focused and maintainable.

Changes

• Updated Chinese README: README.md
• Updated English README: README-EN.md

Kept

• Layered architecture table (responsibility-oriented)
• File-level project structure tree (code-oriented)

Removed

• Overall architecture image module
• Associated architecture-intro text block

Why

• Reduce visual/maintenance overhead in README
• Keep architecture docs concise and implementation-aligned
• Improve readability for contributors who want quick codebase orientation

Impact

• Documentation-only change
• No runtime or API behavior changes

Validation

• Verified both README files render correctly
• Confirmed section structure is consistent in CN/EN docs