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.

test/acceptance/summarize_new_video_test.go

@@ -25,9 +25,11 @@ type fakeSource struct {
 func (f fakeSource) ListSubscriptions(ctx context.Context, userID string) ([]domain.Subscription, error) {
 	return nil, nil
 }
+
 func (f fakeSource) NewVideos(ctx context.Context, sub domain.Subscription) ([]domain.Video, error) {
 	return nil, nil
 }
+
 func (f fakeSource) FetchTranscript(ctx context.Context, v domain.Video) (domain.Transcript, error) {
 	return f.transcript, nil
 }
@@ -132,10 +134,12 @@ type watchSource struct {
 func (s *watchSource) ListSubscriptions(ctx context.Context, userID string) ([]domain.Subscription, error) {
 	return s.subs, nil
 }
+
 func (s *watchSource) NewVideos(ctx context.Context, sub domain.Subscription) ([]domain.Video, error) {
 	s.newVideoHits++
 	return s.videosBySub[sub.ID], nil
 }
+
 func (s *watchSource) FetchTranscript(ctx context.Context, v domain.Video) (domain.Transcript, error) {
 	return s.transcripts[v.ID], nil
 }