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

The six gorm.Open calls in the internal/delivery tests passed a bare
gorm.Config, which installs GORM's default logger; they now pass
gormlog.New over a logger that discards, as every production call does,
so the unfiltered form is no longer in the tree to be copied.

The README and the ParamsFilter comment said (*gorm.DB).Scan had one
test-only caller; there are more. Both now say only tests call it, with
fixture data.

Model: opus-5-5

internal/gormlog/gormlog.go

@@ -111,9 +111,9 @@ func (l *Logger) LogMode(gormlogger.LogLevel) gormlogger.Interface {
 //
 // One GORM path does not consult this: (*gorm.DB).Scan records the
 // statement through gorm's own traceRecorder, which does not implement
-// this interface. No production code path calls it; its one caller is
-// internal/database/database_test.go:91, whose SELECT 1 binds nothing.
-// scan_guard_test.go fails if a non-test file calls it.
+// this interface. No production code path calls it; only tests do, and
+// what a test binds is fixture data. scan_guard_test.go fails if a
+// non-test file calls it.
 // (*gorm.DB).Pluck, Row and Raw all run through the normal callback
 // processor and are filtered.
 func (l *Logger) ParamsFilter(