feat(src/djinit/templates/config/settings): introduce explicit storage configuration

* New Features
  * Replace the singular `STATICFILES_STORAGE` assignment with a `STORAGES` dictionary defining `default` and `staticfiles` backends.

* Enhancements
  * Add `DEFAULT_AUTO_FIELD` setting for consistency with recent Django recommendations.
  * Make storage backend definitions clearer and more extensible.

* Bug Fixes
  * None.

src/djinit/templates/config/settings/base.py-tpl

@@ -112,7 +112,14 @@ STATIC_ROOT = BASE_DIR / "staticfiles"
 MEDIA_URL = "media/"
 MEDIA_ROOT = BASE_DIR / "media"
 
-STATICFILES_STORAGE = "whitenoise.storage.CompressedManifestStaticFilesStorage"
+STORAGES = {
+    "default": {
+        "BACKEND": "django.core.files.storage.FileSystemStorage",
+    },
+    "staticfiles": {
+        "BACKEND": "whitenoise.storage.CompressedManifestStaticFilesStorage",
+    },
+}
 
 DEFAULT_AUTO_FIELD = "django.db.models.BigAutoField"