fix(server): go mod tidy after sync_test brings testify direct

internal/sync/changes_test.go imports github.com/stretchr/testify/require,
moving testify from indirect to direct. Also pulled in testify's own
indirects (go-spew, go-difflib) and promoted pgerrcode to direct.

Caught by CI go vet on 6fb6729.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

go.mod

@@ -6,18 +6,21 @@ require (
 	github.com/dhowden/tag v0.0.0-20240417053706-3d75831295e8
 	github.com/go-chi/chi/v5 v5.2.5
 	github.com/golang-migrate/migrate/v4 v4.18.2
+	github.com/jackc/pgerrcode v0.0.0-20220416144525-469b46aa5efa
 	github.com/jackc/pgx/v5 v5.7.4
+	github.com/stretchr/testify v1.9.0
 	golang.org/x/crypto v0.35.0
 	gopkg.in/yaml.v3 v3.0.1
 )
 
 require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/hashicorp/errwrap v1.1.0 // indirect
 	github.com/hashicorp/go-multierror v1.1.1 // indirect
-	github.com/jackc/pgerrcode v0.0.0-20220416144525-469b46aa5efa // indirect
 	github.com/jackc/pgpassfile v1.0.0 // indirect
 	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
 	github.com/jackc/puddle/v2 v2.2.2 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/rogpeppe/go-internal v1.14.1 // indirect
 	go.uber.org/atomic v1.7.0 // indirect
 	golang.org/x/sync v0.11.0 // indirect