보안: .gitignore에 .env 패턴 추가

Clarify simulation fallback in OAuth guidance

Add API key reassurance and OAuth fallback guidance in block4

Replace /mcp with natural language in block0 setup

Improve onboarding: fix terminology, add MCP troubleshooting, update timing

Fix MCP setup guide: use CLI commands instead of claude.ai/settings

Add MCP setup guides to block4 and pre-setup

Rename skill from /day1-onboarding to /day1

Initial commit: Claude Code onboarding for designers, researchers, and PMs