Implement user authentication system with custom user model, views, and templates

- Created custom User model extending Django's AbstractUser.
- Added user registration, login, and profile views with corresponding templates.
- Implemented user authentication functionality and integrated Bootstrap for styling.
- Updated project settings to use the new accounts app and user model.
- Added tests for user model and admin functionality.

accounts/forms.py

@@ -0,0 +1,36 @@
+from __future__ import annotations
+
+from django.contrib.auth.forms import UserCreationForm
+from django.core.exceptions import ValidationError
+
+from accounts.models import User
+
+
+class CustomUserCreationForm(UserCreationForm):
+    """Custom user creation form for the custom User model."""
+
+    class Meta:
+        model = User
+        fields = ("username",)
+
+    def __init__(self, *args, **kwargs) -> None:
+        """Initialize form with Bootstrap classes."""
+        super().__init__(*args, **kwargs)
+        # Add Bootstrap classes to form fields
+        for field in self.fields.values():
+            field.widget.attrs.update({"class": "form-control"})
+
+    def clean_username(self) -> str:
+        """Validate the username using the correct User model.
+
+        Returns:
+            str: The cleaned username.
+
+        Raises:
+            ValidationError: If the username already exists.
+        """
+        username = self.cleaned_data.get("username")
+        if username and User.objects.filter(username=username).exists():
+            msg = "A user with that username already exists."
+            raise ValidationError(msg)
+        return username or ""