fix(editor): remove a duplicate chat queue translation key (no-changelog)

The key `agents.chat.queue.sendError` was defined two times. JSON parsing
keeps the last entry, which replaced the queue confirmation message.

Also make `planSchema` local again, because no other module imports it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

packages/frontend/@n8n/i18n/src/locales/en.json

@@ -8422,7 +8422,6 @@
 	"agents.chat.tasks.stopped": "Stopped",
 	"agents.chat.tasks.retry": "Retry stopping",
 	"agents.chat.tasks.stopFailedTitle": "Some tasks still need to stop",
-	"agents.chat.queue.sendError": "Couldn’t send the message. Try again.",
 	"agents.chat.plan.title": "Plan: {title}",
 	"agents.chat.plan.progress": "{done} of {total} task done | {done} of {total} tasks done",
 	"agents.chat.plan.viewTrace": "View trace",

packages/frontend/editor-ui/src/features/agents/utils/agent-plan.ts

@@ -22,7 +22,7 @@ const groupSchema = z.object({
 	kind: z.literal('group'),
 	tasks: z.array(taskSchema),
 });
-export const planSchema = z.object({
+const planSchema = z.object({
 	planId: z.string().uuid(),
 	revision: z.number().int().positive(),
 	closed: z.boolean(),