fix(server): wrap defer tx.Rollback for errcheck + gofmt -s alignment

golangci-lint surfaced both on 9c7dec6:
- errcheck on bare 'defer tx.Rollback(ctx)' in 2 test files
- gofmt -s wanted tighter map-key alignment in library_sync.go +
  library_sync_test.go (auto-fixed by 'gofmt -s -w')

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

internal/sync/changes_test.go

@@ -43,7 +43,7 @@ func TestLogChange_WritesRowInTx(t *testing.T) {
 
 	tx, err := pool.Begin(ctx)
 	require.NoError(t, err)
-	defer tx.Rollback(ctx)
+	defer func() { _ = tx.Rollback(ctx) }()
 
 	require.NoError(t, sync.LogChange(ctx, tx, sync.EntityArtist, "artist-123", sync.OpUpsert))
 	require.NoError(t, tx.Commit(ctx))