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/app-server-protocol/src/protocol/v2/item.rs

@@ -902,6 +902,7 @@ impl From<CoreTurnItem> for ThreadItem {
                 id: search.id,
                 query: search.query,
                 action: Some(web_search_action_from_core(search.action)),
+                results: search.results,
             }),
             CoreTurnItem::ImageView(image) => ThreadItem::ImageView {
                 id: image.id,