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/tests.rs

@@ -2777,6 +2777,11 @@ fn core_turn_item_into_thread_item_converts_supported_variants() {
             query: Some("docs".to_string()),
             queries: None,
         },
+        results: Some(vec![serde_json::json!({
+            "type": "text_result",
+            "ref_id": "turn0search0",
+            "url": "https://example.com/docs",
+        })]),
     });
 
     let expected_search_item = WebSearchItem {
@@ -2786,6 +2791,11 @@ fn core_turn_item_into_thread_item_converts_supported_variants() {
             query: Some("docs".to_string()),
             queries: None,
         }),
+        results: Some(vec![serde_json::json!({
+            "type": "text_result",
+            "ref_id": "turn0search0",
+            "url": "https://example.com/docs",
+        })]),
     };
 
     assert_eq!(