Adds server/test/admin-users.test.js and a `npm test` (node --test) script.
No DB_PATH override: the suite mounts the real routers against an isolated
in-memory better-sqlite3 instance injected into the require cache, seeded by
the test itself. Node v20 built-ins only (node:test, node:assert, fetch).
Covers: Add User success (response omits password/hash, hash stored not
plaintext, membership written, hosted lifecycle sentinels stamped, audit row
without the password), duplicate-email 409 (no overwrite), non-admin 403,
platform_operator denied (403), org_admin scoped to their own org only,
input validation, and the must_change_password lifecycle (set on create,
surfaced on login, cleared on PUT /api/auth/me).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
