refactor(output): share the JSON, created-resource and batch tails

Mutations end with a.jsonResult or a.created instead of hand-rolled
--json branches, the two identical jsonResult/writeMutationJSON helpers
become one, and writeBatchJSON checks --json itself so batch commands
share one tail.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/milestone_state.go

@@ -50,11 +50,8 @@ $ tea milestone %[1]s v1.0 v1.1`, verb), Annotations: map[string]string{"tea.arg
 				a.done(cmd, "%s %s", past, milestoneName(t, item))
 			}
 			return item, err
-		}, func(services.Milestone) {})
-		if a.options.json != "" {
-			failures = append(failures, writeBatchJSON(a, cmd, len(selected), results))
-		}
-		return errors.Join(failures...)
+		}, nil)
+		return errors.Join(append(failures, writeBatchJSON(a, cmd, len(selected), results))...)
 	}}
 	cmd.Flags().BoolVar(&byName, "by-name", false, "Match numeric arguments as milestone titles rather than IDs")
 	cmd.ValidArgsFunction = a.completeMilestoneArgs(true)