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/app/core/config.py

@@ -2,6 +2,7 @@
 Application configuration using Pydantic settings.
 Supports environment variables and .env files.
 """
+
 from typing import Optional, List
 from pydantic_settings import BaseSettings, SettingsConfigDict
 from pydantic import PostgresDsn, field_validator, ValidationInfo
@@ -9,86 +10,85 @@ from pydantic import PostgresDsn, field_validator, ValidationInfo
 
 class Settings(BaseSettings):
     """Application settings loaded from environment variables"""
-    
+
     model_config = SettingsConfigDict(
-        env_file=".env",
-        env_file_encoding="utf-8",
-        case_sensitive=False,
-        extra="ignore"
+        env_file=".env", env_file_encoding="utf-8", case_sensitive=False, extra="ignore"
     )
-    
+
     # Application
     APP_NAME: str = "POP3 Forwarder SaaS"
     APP_VERSION: str = "2.0.0"
     DEBUG: bool = False
     API_V1_PREFIX: str = "/api/v1"
-    
+
     # Server
     HOST: str = "0.0.0.0"
     PORT: int = 8000
-    
+
     # Database
-    DATABASE_URL: str = "postgresql+asyncpg://user:password@localhost:5432/pop3_forwarder"
+    DATABASE_URL: str = (
+        "postgresql+asyncpg://user:password@localhost:5432/pop3_forwarder"
+    )
     DATABASE_POOL_SIZE: int = 20
     DATABASE_MAX_OVERFLOW: int = 10
-    
+
     # Security
     SECRET_KEY: str = "change-this-to-a-secure-random-secret-key-in-production"
     ALGORITHM: str = "HS256"
     ACCESS_TOKEN_EXPIRE_MINUTES: int = 30
     REFRESH_TOKEN_EXPIRE_DAYS: int = 7
-    
+
     # Encryption (for storing POP3/IMAP credentials)
     ENCRYPTION_KEY: str = "change-this-to-a-secure-encryption-key"
-    
+
     # OAuth2 - Google
     GOOGLE_CLIENT_ID: Optional[str] = None
     GOOGLE_CLIENT_SECRET: Optional[str] = None
     GOOGLE_REDIRECT_URI: str = "http://localhost:3000/auth/callback/google"
-    
+
     # Gmail API (for direct email injection)
     GMAIL_API_ENABLED: bool = True
     GMAIL_INJECT_LABEL_IDS: List[str] = ["INBOX"]
-    
+
     # CORS
     CORS_ORIGINS: List[str] = ["http://localhost:3000", "http://localhost:8000"]
-    
+
     # Stripe Payment
     STRIPE_API_KEY: Optional[str] = None
     STRIPE_WEBHOOK_SECRET: Optional[str] = None
     STRIPE_PUBLISHABLE_KEY: Optional[str] = None
-    
+
     # Subscription Tiers
     TIER_FREE_MAX_ACCOUNTS: int = 1
     TIER_BASIC_MAX_ACCOUNTS: int = 5
     TIER_PRO_MAX_ACCOUNTS: int = 20
     TIER_ENTERPRISE_MAX_ACCOUNTS: int = 100
-    
+
     # Email Processing
     MAX_EMAILS_PER_RUN: int = 50
     CHECK_INTERVAL_MINUTES: int = 5
     THROTTLE_EMAILS_PER_MINUTE: int = 10
-    
+
     # Redis (for Celery and caching)
     REDIS_URL: str = "redis://localhost:6379/0"
-    
+
     # Celery
     CELERY_BROKER_URL: str = "redis://localhost:6379/0"
     CELERY_RESULT_BACKEND: str = "redis://localhost:6379/0"
-    
+
     # Apprise (notifications)
     APPRISE_ENABLED: bool = True
-    
+
     # Logging
     LOG_LEVEL: str = "INFO"
-    
+
     # Admin
     ADMIN_EMAIL: Optional[str] = None
     ADMIN_PASSWORD: Optional[str] = None
-    
+
     # Mail Server Presets
     MAIL_SERVER_PRESETS_FILE: str = "app/data/mail_server_presets.json"
-    
+
     @field_validator("CORS_ORIGINS", mode="before")
     @classmethod
     def assemble_cors_origins(cls, v: str | List[str]) -> List[str]:
@@ -96,7 +96,7 @@ class Settings(BaseSettings):
         if isinstance(v, str):
             return [i.strip() for i in v.split(",")]
         return v
-    
+
     @field_validator("SECRET_KEY")
     @classmethod
     def validate_secret_key(cls, v: str) -> str:
@@ -118,7 +118,7 @@ class Settings(BaseSettings):
                 "Generate a secure key with: python -c 'import secrets; print(secrets.token_urlsafe(32))'"
             )
         return v
-    
+
     @field_validator("ENCRYPTION_KEY")
     @classmethod
     def validate_encryption_key(cls, v: str) -> str: