docs: prepare design-workflow v0.2.2

[sleegme]

Summary

• explain in plain language what design-workflow changes after installation and what it does not do
• document compatible ChatGPT upload, macOS/Windows expectations, separate Codex installation, a verification prompt, and first-user FAQ in English and Korean
• bump the release source of truth and changelog to 0.2.2
• make tagged release reruns replace existing ZIP and checksum assets instead of failing on an existing GitHub Release

Why

Early users expected installation to alter every visual result and lacked clear ChatGPT installation guidance. Separately, the release workflow always called gh release create, so rerunning a successful tagged build failed once the release already existed even though validation and packaging had succeeded.

This patch makes onboarding expectations explicit and makes release asset publication idempotent without deleting or recreating tags. It preserves the existing meaningful_design_exists routing contract and does not include the visual-quality work tracked in #8.

Validation

• python scripts/validate_project.py
• agentskills validate design-workflow
• python -m unittest discover -s tests -v (22 tests)
• deterministic skill archive comparison
• deterministic project archive comparison
• git diff --check

Closes #7