[Copilot]

The Admin User Management page displayed empty tables across all three tabs (Admins, Active Students, Inactive Students) even when users existed in the database.

Root causes

• database/user.go — ListUsers() used var users []*models.User (nil slice), which json.Encode serializes as null. The JS client then called .length on null or silently iterated zero times, leaving tables empty.

  // Before: nil → JSON null
  var users []*models.User
  
  // After: always a JSON array []
  users := make([]*models.User, 0)

• static/js/admin/users.js — No guard against a non-array API response; any unexpected value caused silent failure.

  const rawUsers = await API.get('/admin/users');
  const users = Array.isArray(rawUsers) ? rawUsers : [];

• static/sw.js — Service worker stale-while-revalidate could serve old cached JS to returning users. Bumped CACHE_NAME from athena-v9 → athena-v10 to evict stale files on next load.

• api/auth.go — RegisterHandler bypassed h.db.CreateUser() with a raw SQL INSERT that omitted the category column. Refactored to use the interface method, which includes all columns and sets category: "java" explicitly (matching the existing DB default; admins can update it via the User Management page).