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/adventure_flavor_dungeon.go

@@ -924,4 +924,4 @@ var DungeonExceptional = map[int][]string{
 			"in a dungeon. Write it down. " +
 			"The dungeon will tell this story differently.",
 	},
-}
+}