style: apply gofumpt

Estate-wide consolidation pass. The canonical .golangci.yml
(infra ci-templates/golangci.yml, infra#309 pattern) enables the gofumpt
formatter; golangci-lint v2 default set enables NO formatter, which is why
this drift accumulated silently -- the same hole that let two files rot in
dma-cli until they were found by hand (dma-cli#12).

Mechanical and deterministic: `gofumpt -w .`, nothing hand-edited. Verified
per repo before commit -- gofumpt -l now reports 0, gofmt -l reports 0, and
go build + go vet both pass.

Clears this repo to adopt the canonical lint config in a later wave.

internal/web/visual_theme_test.go

@@ -14,7 +14,8 @@ import (
 // page renders any GET path's full HTML (helper for theme/structure assertions).
 func page(t *testing.T, app interface {
 	Router() http.Handler
-}, path string) string {
+}, path string,
+) string {
 	t.Helper()
 	rec := httptest.NewRecorder()
 	app.Router().ServeHTTP(rec, httptest.NewRequest(http.MethodGet, path, nil))