Фаза 2, Task 1: добавлена таблица sessions и nullable password_hash у
users, sqlc-запросы и *Store-обёртки (CreateUser, GetUserByEmail,
CreateProjectForUser, GetProjectOwned, GetUserProject, CreateSession,
GetSessionUser, DeleteSession, RegisterUser в транзакции), интеграционные
тесты на testcontainers.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BwxdSt4reTm7Dj1oxRvpP3
