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_config.py

@@ -1,6 +1,7 @@
 """
 Unit tests for configuration module.
 """
+
 import pytest
 from pydantic import ValidationError
 from app.core.config import Settings
@@ -8,7 +9,7 @@ from app.core.config import Settings
 
 class TestConfigValidation:
     """Test configuration validation"""
-    
+
     def test_default_secret_key_rejected(self):
         """Test that default SECRET_KEY is rejected"""
         with pytest.raises(ValidationError) as exc_info:
@@ -16,9 +17,9 @@ class TestConfigValidation:
                 SECRET_KEY="change-this-to-a-secure-random-secret-key-in-production",
                 ENCRYPTION_KEY="this-is-a-secure-32-character-key-for-testing",
             )
-        
+
         assert "SECRET_KEY must be changed from default" in str(exc_info.value)
-    
+
     def test_short_secret_key_rejected(self):
         """Test that short SECRET_KEY is rejected"""
         with pytest.raises(ValidationError) as exc_info:
@@ -26,9 +27,9 @@ class TestConfigValidation:
                 SECRET_KEY="short",
                 ENCRYPTION_KEY="this-is-a-secure-32-character-key-for-testing",
             )
-        
+
         assert "at least 32 characters" in str(exc_info.value)
-    
+
     def test_default_encryption_key_rejected(self):
         """Test that default ENCRYPTION_KEY is rejected"""
         with pytest.raises(ValidationError) as exc_info:
@@ -36,9 +37,9 @@ class TestConfigValidation:
                 SECRET_KEY="this-is-a-secure-32-character-key-for-testing",
                 ENCRYPTION_KEY="change-this-to-a-secure-encryption-key",
             )
-        
+
         assert "ENCRYPTION_KEY must be changed from default" in str(exc_info.value)
-    
+
     def test_short_encryption_key_rejected(self):
         """Test that short ENCRYPTION_KEY is rejected"""
         with pytest.raises(ValidationError) as exc_info:
@@ -46,15 +47,21 @@ class TestConfigValidation:
                 SECRET_KEY="this-is-a-secure-32-character-key-for-testing",
                 ENCRYPTION_KEY="short",
             )
-        
+
         assert "at least 32 characters" in str(exc_info.value)
-    
+
     def test_valid_keys_accepted(self):
         """Test that valid keys are accepted"""
         settings = Settings(
             SECRET_KEY="this-is-a-secure-32-character-key-for-testing-secret",
             ENCRYPTION_KEY="this-is-a-secure-32-character-key-for-encryption",
         )
-        
-        assert settings.SECRET_KEY == "this-is-a-secure-32-character-key-for-testing-secret"
-        assert settings.ENCRYPTION_KEY == "this-is-a-secure-32-character-key-for-encryption"
+
+        assert (
+            settings.SECRET_KEY
+            == "this-is-a-secure-32-character-key-for-testing-secret"
+        )
+        assert (
+            settings.ENCRYPTION_KEY
+            == "this-is-a-secure-32-character-key-for-encryption"
+        )