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
 

webvirtcloud/settings.py.template

@@ -161,9 +161,9 @@ else:
             "NAME": Path.joinpath(BASE_DIR, "db.sqlite3"),
             # IMMEDIATE takes the write lock when a transaction starts, so a
             # check-then-write cannot interleave with another process; timeout
-            # is how long a writer waits for that lock (seconds). WAL is set
-            # per connection by the operations app.
-            "OPTIONS": {"transaction_mode": "IMMEDIATE", "timeout": 20},
+            # is how long a writer waits for that lock (seconds). WAL lets the
+            # worker and gunicorn read while one of them writes.
+            "OPTIONS": {"transaction_mode": "IMMEDIATE", "timeout": 20, "init_command": "PRAGMA journal_mode=WAL"},
             # A file, not shared-cache memory: test threads and worker processes
             # open the same database, and shared-cache locks ignore the timeout.
             "TEST": {"NAME": os.getenv("WEBVIRTCLOUD_TEST_DB") or Path.joinpath(BASE_DIR, "test_db.sqlite3")},