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

README.md

@@ -2609,11 +2609,10 @@ on all three arms of `Trace`, including the routine one an operator
 reaches at `DEBUG`, which is the only level at which a successful
 `INSERT` is written at all. One GORM path does not consult the filter —
 `(*gorm.DB).Scan`, which records the statement through GORM's own trace
-recorder. No production code path calls it; its one caller is
-`internal/database/database_test.go:91`, whose `SELECT 1` binds
-nothing, and `internal/gormlog/scan_guard_test.go` fails if a non-test
-file calls it. `Pluck`, `Row` and `Raw` all run through the normal
-callback processor and are filtered.
+recorder. No production code path calls it; only tests do, and what a
+test binds is fixture data. `internal/gormlog/scan_guard_test.go` fails
+if a non-test file calls it. `Pluck`, `Row` and `Raw` all run through
+the normal callback processor and are filtered.
 See `#### What DEBUG=true exposes` under Configuration.
 
 What that ceiling does **not** cover, stated here so the figure is not