Route the delivery tests' gorm.Open through gormlog (closes #462)

Six test-only gorm.Open calls in internal/delivery passed a bare gorm.Config, leaving the unfiltered idiom in the tree to be copied into production code, where every gorm.Open goes through gormlog.New. They now pass gormlog.New over a logger that discards, so no gorm.Open in the tree uses a bare gorm.Config. The stale sentence saying the tree has one test-only (*gorm.DB).Scan caller is corrected in the README and in the ParamsFilter comment: only tests call Scan, and what a test binds is fixture data. Test and documentation change only.

Model: opus-5-5

internal/delivery/engine_test.go

@@ -26,6 +26,7 @@ import (
 	_ "modernc.org/sqlite"
 	"sneak.berlin/go/webhooker/internal/database"
 	"sneak.berlin/go/webhooker/internal/delivery"
+	"sneak.berlin/go/webhooker/internal/gormlog"
 	"sneak.berlin/go/webhooker/internal/metrics"
 )
 
@@ -50,7 +51,8 @@ func testWebhookDB(t *testing.T) *gorm.DB {
 	t.Cleanup(func() { _ = sqlDB.Close() })
 
 	db, err := gorm.Open(
-		sqlite.Dialector{Conn: sqlDB}, &gorm.Config{},
+		sqlite.Dialector{Conn: sqlDB},
+		&gorm.Config{Logger: gormlog.New(slog.New(slog.DiscardHandler))},
 	)
 	require.NoError(t, err)