docs: 시스템 아키텍처 및 명령어 문서 추가

- COMMAND.md: 다양한 명령어와 설명 추가
- .claude/commands/design/1-system-architecture: 시스템 아키텍처 관련 문서 삭제
- .claude/commands/sc: 코드 분석, 빌드, 클린업, 설계, 문서화, 추정, 설명, Git 작업, 구현, 개선, 테스트, 문제 해결, 워크플로우 생성 등 다양한 명령어 문서 추가

.claude/commands/sc/explain.md

@@ -0,0 +1,33 @@
+---
+allowed-tools: [Read, Grep, Glob, Bash]
+description: "Provide clear explanations of code, concepts, or system behavior"
+---
+
+# /sc:explain - Code and Concept Explanation
+
+## Purpose
+Deliver clear, comprehensive explanations of code functionality, concepts, or system behavior.
+
+## Usage
+```
+/sc:explain [target] [--level basic|intermediate|advanced] [--format text|diagram|examples]
+```
+
+## Arguments
+- `target` - Code file, function, concept, or system to explain
+- `--level` - Explanation complexity (basic, intermediate, advanced)
+- `--format` - Output format (text, diagram, examples)
+- `--context` - Additional context for explanation
+
+## Execution
+1. Analyze target code or concept thoroughly
+2. Identify key components and relationships
+3. Structure explanation based on complexity level
+4. Provide relevant examples and use cases
+5. Present clear, accessible explanation with proper formatting
+
+## Claude Code Integration
+- Uses Read for comprehensive code analysis
+- Leverages Grep for pattern identification
+- Applies Bash for runtime behavior analysis
+- Maintains clear, educational communication style