Expose structured standalone web search results (#32898)

## Why

Standalone web search can return structured result DTOs separately from its
model-facing text output. App-server clients need access to that data without
coupling Codex to every result type or field.

## What changed

- Preserve the optional `results` array from `/v1/alpha/search` as opaque JSON
  through web-search completion events, thread history, and app-server
  `webSearch` items.
- Keep responses from older endpoints compatible when `results` is absent, and
  allow clients to ignore result types and fields they do not understand.
- Regenerate the protocol schemas and TypeScript definitions for the optional
  field.

## Testing

- Cover responses with missing, empty, and forward-compatible result payloads.
- Verify standalone web-search results round-trip through app-server item
  notifications and thread-item conversion.

GitOrigin-RevId: 739ef5694ece5733f7b8749ec41d6bfa3f33c8c5

codex-rs/analytics/src/analytics_client_tests.rs

@@ -4421,6 +4421,7 @@ async fn turn_event_counts_completed_tool_items() {
             id: "web-1".to_string(),
             query: "codex".to_string(),
             action: None,
+            results: None,
         }),
         ThreadItem::ImageGeneration(ImageGenerationItem {
             id: "image-1".to_string(),