style: apply black and isort formatting across entire codebase

- Standardize quote style (single to double quotes)
- Reorder and group imports alphabetically
- Fix line breaks and indentation for consistency
- Apply PEP 8 formatting standards

Also updated Makefile to exclude both venv and .venv from code quality checks.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/exceptions/auth.py

@@ -4,7 +4,9 @@ Authentication and authorization specific exceptions.
 """
 
 from typing import Optional
-from .base import AuthenticationException, AuthorizationException, ConflictException
+
+from .base import (AuthenticationException, AuthorizationException,
+                   ConflictException)
 
 
 class InvalidCredentialsException(AuthenticationException):
@@ -41,9 +43,9 @@ class InsufficientPermissionsException(AuthorizationException):
     """Raised when user lacks required permissions for an action."""
 
     def __init__(
-            self,
-            message: str = "Insufficient permissions for this action",
-            required_permission: Optional[str] = None,
+        self,
+        message: str = "Insufficient permissions for this action",
+        required_permission: Optional[str] = None,
     ):
         details = {}
         if required_permission:
@@ -80,9 +82,9 @@ class UserAlreadyExistsException(ConflictException):
     """Raised when trying to register with existing username/email."""
 
     def __init__(
-            self,
-            message: str = "User already exists",
-            field: Optional[str] = None,
+        self,
+        message: str = "User already exists",
+        field: Optional[str] = None,
     ):
         details = {}
         if field: