docs: comprehensive README update with VS Code, Connect, and full usa…

…ge guide

Both English and Korean READMEs now cover:
- VS Code extension installation and usage
- DiffMind Connect (LLM, GitHub, Slack, Discord)
- All CLI commands with options tables
- Architecture diagram
- Settings reference
- CI/CD integration examples

Co-Authored-By: Claude Opus 4.6 <[email protected]>