refactor(frontend): remove unused response envelope schema (#6204)

Co-authored-by: n0ctal <[email protected]>

frontend/src/schemas/_envelope.ts

@@ -1,10 +0,0 @@
-import { z } from 'zod';
-
-export const msgSchema = <T extends z.ZodType>(obj: T) =>
-  z.object({
-    success: z.boolean(),
-    msg: z.string().default(''),
-    obj: obj.nullable(),
-  });
-
-export type MsgOf<S extends z.ZodType> = z.infer<ReturnType<typeof msgSchema<S>>>;