Replace sensitive token fragments in structured logs with:
- login(): Use session_id=session.id (database row ID) instead of token_prefix
- logout(): Use token_hash (SHA256 one-way hash, first 12 chars) instead of token_prefix
This prevents partial token material leakage into log aggregation systems while
maintaining useful session correlation via hashed tokens or database IDs.
Also updated Backend-Development.md to clarify logging conventions for
sensitive data handling.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>