refactor(settings): SQLite's WAL mode is an init_command

The operations app set PRAGMA journal_mode=WAL from a connection_created
receiver because Django's SQLite OPTIONS had no init command; Django 5.1
added init_command, so the template sets it there and the receiver goes.
The mode is stored in the database file, so existing databases keep it.

operations/apps.py

@@ -1,21 +1,10 @@
 from django.apps import AppConfig
-from django.db.backends.signals import connection_created
-
-
-def _sqlite_wal(sender, connection, **kwargs):
-    """The worker and gunicorn write the same SQLite file: WAL lets readers
-    go on during a write. Django's SQLite OPTIONS have no init command."""
-    if connection.vendor == "sqlite":
-        with connection.cursor() as cursor:
-            cursor.execute("PRAGMA journal_mode=WAL")
 
 
 class OperationsConfig(AppConfig):
-    default_auto_field = "django.db.models.BigAutoField"
     name = "operations"
 
     def ready(self):
-        connection_created.connect(_sqlite_wal)
         # every installed app's jobs.py registers its kinds
         from django.utils.module_loading import autodiscover_modules