Fix code formatting and linting issues

- Auto-format all Python files with black and isort
- Remove unused imports with autoflake
- Fix flake8 issues (missing newlines, blank lines, etc.)
- Fix nonlocal/global scope issues in main.py
- Fix security.py import order (E402)
- Remove f-string without placeholders
- Add nosec comment for intentional exception handling
- Fix test imports to match refactored DMARCParser API

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

backend/app/models/user.py

@@ -1,13 +1,12 @@
-from typing import List, Optional
-from sqlalchemy import Boolean, Column, Integer, String
-from sqlalchemy.orm import relationship
 
 from app.core.database import Base
+from sqlalchemy import Boolean, Column, Integer, String
+from sqlalchemy.orm import relationship
 
 
 class User(Base):
     """User model"""
-    
+
     __tablename__ = "users"
 
     id = Column(Integer, primary_key=True, index=True)
@@ -16,10 +15,10 @@ class User(Base):
     is_active = Column(Boolean, default=True)
     is_superuser = Column(Boolean, default=False)
     is_verified = Column(Boolean, default=False)
-    
+
     # Additional fields
     full_name = Column(String, nullable=True)
     organization = Column(String, nullable=True)
-    
+
     # Relationships
-    user_domains = relationship("UserDomain", back_populates="user", cascade="all, delete-orphan")
+    user_domains = relationship("UserDomain", back_populates="user", cascade="all, delete-orphan")