gofmt: bring internal/ and cmd/ back to gofmt -l clean

Mechanical `gofmt -w ./internal ./cmd`. Mostly struct-field realignment that
had drifted, plus a few trailing-newline fixes. No behaviour change — gofmt is
semantics-preserving, and build/vet/test are green either side.

Split out from the code-review fixes that follow so those stay reviewable
instead of hiding inside a wall of realignment.

internal/plugin/dnd_plugs_test.go

@@ -112,9 +112,9 @@ func TestDnDRollSummaryLine_HighestNonNat20(t *testing.T) {
 
 func TestParseDice(t *testing.T) {
 	cases := []struct {
-		in                          string
-		count, sides, mod           int
-		ok                          bool
+		in                string
+		count, sides, mod int
+		ok                bool
 	}{
 		{"d20", 1, 20, 0, true},
 		{"1d20", 1, 20, 0, true},