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

apibase/env.py

@@ -0,0 +1,6 @@
+import environ
+from pathlib import Path
+
+env = environ.Env()
+
+BASE_DIR = Path(__file__).resolve().parent.parent