feat: implement complete CMT backend with API endpoints and test suite

- Add 7 core API endpoints: users, transactions, partners, products, inventory, payments, credit
- Implement role-based authentication (admin/write/read-only access)
- Add comprehensive database models with proper relationships
- Include full test coverage for all endpoints and business logic
- Set up Alembic migrations and Docker configuration
- Configure FastAPI app with CORS and database integration

backend/app/core/config.py

@@ -6,10 +6,20 @@ from pydantic_settings import BaseSettings, SettingsConfigDict
 
 class Settings(BaseSettings):
     """
+    Application settings loaded from environment variables.
     """
     database_uri: PostgresDsn
     environment: str
     project_name: str
+    
+    # JWT settings
+    secret_key: str = "your-secret-key-change-this-in-production"
+    algorithm: str = "HS256"
+    
+    # Role-based expiration times (in minutes)
+    admin_token_expire_minutes: int = 60 * 24 * 7  # 7 days (default)
+    write_token_expire_minutes: int = 60 * 24 * 3  # 3 days (default)
+    read_only_token_expire_minutes: int = 60 * 8   # 8 hours (default)
 
     model_config = SettingsConfigDict(
         # One level above ./backend