🔒 security: move IMAP credentials to request body and fix CI/pylint issues

- Moved IMAP credentials from query parameters to the request body for the test-connection endpoint.
- Created missing `__init__.py` files across `backend/app/` to fix CI `ModuleNotFoundError`.
- Reformatted `setup.py` and `user.py` using `black` to pass lint checks.
- Addressed Pylint warnings in `imap.py` (unused arguments, lazy logging, exception chaining).

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

backend/app/models/user.py

@@ -1,8 +1,8 @@
-
-from app.core.database import Base
 from sqlalchemy import Boolean, Column, Integer, String
 from sqlalchemy.orm import relationship
 
+from app.core.database import Base
+
 
 class User(Base):
     """User model"""