Refactor Django settings module and environment configuration

- Move settings to a modular configuration structure
- Update environment variables in .env.example
- Modify DJANGO_SETTINGS_MODULE references across project files
- Simplify and standardize environment variable naming

manage.py

@@ -7,7 +7,7 @@ import sys
 
 def main():
     """Run administrative tasks."""
-    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "apibase.settings")
+    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "apibase.django.local")
     try:
         from django.core.management import execute_from_command_line
     except ImportError as exc: