63 tests across 8 spec files, all passing. Removes 2 stale stub files from
backend/test/ that were incompatible with the current async EncryptionService
and 3-argument AuthService constructor. New suite lives in src/ co-located
with source files per NestJS convention.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
