Merge origin/pre/v2.1 into fix/postgresql-adapter-bugs

Resolved conflicts in:
- src/datajoint/adapters/postgres.py
- src/datajoint/declare.py
- src/datajoint/dependencies.py

Kept PostgreSQL adapter fixes and backend-specific query implementations.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dimitri-yatsenko