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/euro.go

@@ -583,4 +583,3 @@ func (p *EuroPlugin) handleGrant(ctx MessageContext) error {
 	return p.SendReply(ctx.RoomID, ctx.EventID,
 		fmt.Sprintf("✅ Granted €%d to **%s**. New balance: €%d.", int(amount), targetName, int(newBalance)))
 }
-