feat(djinit/templates/project): default DJANGO_SETTINGS_MODULE to project production settings

Set the default DJANGO_SETTINGS_MODULE environment variable to point to the production settings module derived from the project name, ensuring the Django management script runs with the correct configuration when no explicit DJANGO_SETTINGS_MODULE is provided.

New Features
- Automatically default the DJANGO_SETTINGS_MODULE to `<project_name>.settings.production`, simplifying project setup.

Enhancements
- Improves the management script initialization by providing a sensible production settings fallback.

Bug Fixes
- None.

djinit/templates/project/manage_py.j2

@@ -11,7 +11,7 @@ import environ
 
 def main():
     """Run administrative tasks."""
-    os.environ.setdefault("DJANGO_SETTINGS_MODULE", os.getenv("DJANGO_SETTINGS_MODULE"))
+    os.environ.setdefault("DJANGO_SETTINGS_MODULE", os.getenv("DJANGO_SETTINGS_MODULE", "{{ project_name }}.settings.production"))
 
     try:
         from django.core.management import execute_from_command_line