fix(db): do not log the database password - #204

Types of changes

• Bugfix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality not to work as expected).
• Documentation Update (if none of the other choices applies).

Proposed changes

src/database/session.py logged the full connection string at DEBUG, password included. It now logs the engine URL with repr(), which masks the password:

Database URL: mariadb+asyncmy://bot:***@localhost:3306/bot_dev?charset=utf8mb4

Checklist

• I have read and followed the CONTRIBUTING.md
  doc.
• Lint and unit tests pass locally with my changes.
• I have added the necessary documentation (if appropriate).

Additional context

tests/src/database/test_session.py reloads the module with a known password and checks that it does not appear in the logs. It failed before the fix.