Adds /api/users endpoints (admin only) plus /api/users/assignable
(admin + technician) used by the aftersales reassign picker. Guards
prevent self-demotion, self-deletion, and removing the last admin.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
User-requested format: zjbf-sh-260501 (26=year, 05=month, 01=monthly seq).
Sequence resets each month and skips soft-deleted entries to avoid reuse.
Also documents aftersales API and new technician role in AGENTS.md / README.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>