Gemini CLI에 서브에이전트 기능 도입

Gemini CLI's new multi-agent architecture enables developers to delegate complex tasks to specialized sub-agents with isolated context windows and independent toolsets, significantly accelerating development workflows. The parallel execution capability allows simultaneous processing of research, refactoring, and code analysis tasks while preventing context pollution in the main session. Custom sub-agents defined in markdown with YAML frontmatter can be easily shared across teams, providing extensible and collaborative development capabilities.