Fix CI failures: add backend/conftest.py for module resolution and run black formatting

- Add backend/conftest.py that inserts the backend directory into sys.path,
  fixing ModuleNotFoundError when pytest runs from the backend/ directory
  (as CI does with `cd backend && pytest tests/`)
- Run black formatter on all 28 backend files that needed reformatting
- All 53 tests pass with both `pytest tests/` and `python -m pytest tests/`

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>
Agent-Logs-Url: https://github.com/christianlouis/pop_puller_to_gmail/sessions/beb47db2-da25-416a-8fb0-c1452a3b22a7

backend/tests/unit/test_security.py

@@ -1,6 +1,7 @@
 """
 Unit tests for security module.
 """
+
 import pytest
 from app.core.security import (
     get_password_hash,
@@ -12,99 +13,99 @@ from app.core.security import (
 
 class TestPasswordHashing:
     """Test password hashing and verification"""
-    
+
     def test_hash_password(self):
         """Test password hashing"""
         password = "securepassword123"
         hashed = get_password_hash(password)
-        
+
         assert hashed != password
         assert len(hashed) > 50
         assert hashed.startswith("$2b$")
-    
+
     def test_verify_password_success(self):
         """Test password verification with correct password"""
         password = "securepassword123"
         hashed = get_password_hash(password)
-        
+
         assert verify_password(password, hashed) is True
-    
+
     def test_verify_password_failure(self):
         """Test password verification with wrong password"""
         password = "securepassword123"
         wrong_password = "wrongpassword"
         hashed = get_password_hash(password)
-        
+
         assert verify_password(wrong_password, hashed) is False
 
 
 class TestJWT:
     """Test JWT token creation and validation"""
-    
+
     def test_create_access_token(self):
         """Test access token creation"""
         data = {"sub": "test@example.com"}
         token = create_access_token(data)
-        
+
         assert isinstance(token, str)
         assert len(token) > 50
-        assert token.count('.') == 2  # JWT has 3 parts
+        assert token.count(".") == 2  # JWT has 3 parts
 
 
 class TestEncryption:
     """Test credential encryption/decryption"""
-    
+
     def test_encrypt_password(self):
         """Test password encryption"""
         password = "mailpassword123"
         user_id = 1
-        
+
         encryptor = CredentialEncryption(user_id=user_id)
         encrypted = encryptor.encrypt(password)
-        
+
         assert encrypted != password
         assert len(encrypted) > 50
-    
+
     def test_decrypt_password(self):
         """Test password decryption"""
         password = "mailpassword123"
         user_id = 1
-        
+
         encryptor = CredentialEncryption(user_id=user_id)
         encrypted = encryptor.encrypt(password)
         decrypted = encryptor.decrypt(encrypted)
-        
+
         assert decrypted == password
-    
+
     def test_encryption_with_different_user_ids(self):
         """Test that encryption produces different results for different users"""
         password = "mailpassword123"
         user_id_1 = 1
         user_id_2 = 2
-        
+
         encryptor_1 = CredentialEncryption(user_id=user_id_1)
         encryptor_2 = CredentialEncryption(user_id=user_id_2)
-        
+
         encrypted_1 = encryptor_1.encrypt(password)
         encrypted_2 = encryptor_2.encrypt(password)
-        
+
         # Different users should produce different encrypted values
         assert encrypted_1 != encrypted_2
-        
+
         # But decryption should work correctly for each
         assert encryptor_1.decrypt(encrypted_1) == password
         assert encryptor_2.decrypt(encrypted_2) == password
-    
+
     def test_decrypt_with_wrong_user_id_fails(self):
         """Test that decryption fails with wrong user ID"""
         password = "mailpassword123"
         user_id = 1
         wrong_user_id = 2
-        
+
         encryptor = CredentialEncryption(user_id=user_id)
         wrong_encryptor = CredentialEncryption(user_id=wrong_user_id)
-        
+
         encrypted = encryptor.encrypt(password)
-        
+
         with pytest.raises(Exception):
             wrong_encryptor.decrypt(encrypted)