feat(src/djinit/templates/project): load .env and use env for settings module

Replace hard‑coded settings module with environment variable and load .env configuration for smoother local development.

src/djinit/templates/project/manage.py-tpl

@@ -5,13 +5,21 @@
 """Django's command-line utility for administrative tasks."""
 import os
 import sys
+from pathlib import Path
 
 import environ
 
+env_path = Path(__file__).resolve().parent.parent / ".env"
+env = environ.Env()
+environ.Env.read_env(env_path)
+
 
 def main():
     """Run administrative tasks."""
-    os.environ.setdefault("DJANGO_SETTINGS_MODULE", os.getenv("DJANGO_SETTINGS_MODULE", "[[ project_name ]].settings.production"))
+    os.environ.setdefault(
+        "DJANGO_SETTINGS_MODULE",
+        env("DJANGO_SETTINGS_MODULE", default="[[ project_name ]].settings.production"),
+    )
 
     try:
         from django.core.management import execute_from_command_line