Expose image generation usage-limit failures (#38024)

## What changed

- Add structured `usageLimitExceeded` metadata to failed image-generation
  items, including the image limit ID and optional reset timestamp.
- Preserve the failure metadata in completion events, app-server thread
  history, thread reads and resumes, and migrated legacy rollouts.
- Export the new failure type in the generated JSON and TypeScript schemas.

## Testing

- Cover usage-limit responses through item completion, persistence, and thread
  resume.
- Verify legacy rollout migration retains image-generation failure metadata.

GitOrigin-RevId: 91c31a2a47456b6b916ee03002ff314b05946dd4

codex-rs/analytics/src/analytics_client_tests.rs

@@ -4787,6 +4787,7 @@ async fn turn_event_counts_completed_tool_items() {
             revised_prompt: None,
             result: "ok".to_string(),
             transparent_background: None,
+            failure: None,
             saved_path: None,
         }),
     ];