Add hint property to PublishAgentsErrorResponse schema

This enables the npm-app CLI to display helpful hints when agent
publishing fails, improving the developer experience.

🤖 Generated with Codebuff
Co-Authored-By: Codebuff <noreply@codebuff.com>

Author: brandonkachen

common/src/types/api/agents/publish.ts

@@ -27,6 +27,7 @@ export const publishAgentsErrorResponseSchema = z.object({
   success: z.literal(false),
   error: z.string(),
   details: z.string().optional(),
+  hint: z.string().optional(),
   availablePublishers: z
     .object({
       id: z.string(),