Track homepage and site improvements

[Seungpyo1007]

Persistent tracker for TechAPI homepage and public site work. Keep this issue open while site, playground, history, and deployment polish continues.

Current focus:

• Homepage Playground naming and history section
• PR-time homepage validation through TechEngineBot
• Site metadata automation for future PRs
• Dataset growth history polish

This is a long-running tracker. Do not close it from normal site PR merges.

[Seungpyo1007]

Reopening this persistent site tracker. Site work is still ongoing, so future homepage PRs should reference it without closing it.