Forward thread originators from standalone extensions (#33677)

## Why

Standalone web search and image requests need to preserve the trusted,
thread-scoped originator used for billing attribution.

## What changed

- Seed extension data with the resolved thread originator and recognize
  `codex_work_cca` and `chatgpt_cca` service names as originators.
- Forward non-default originators from the web search and image generation
  extensions with the shared originator-header helper.

## Testing

- Cover originator resolution, header validation, and forwarding for web
  search, image generation, and image editing.

GitOrigin-RevId: 165dace8e4d24e4bd92f234bff5ec77a21a7ff6e

codex-rs/core/src/session/session.rs

@@ -583,6 +583,9 @@ impl Session {
                     roots
                 }
             };
+        thread_extension_init.insert(codex_extension_api::ThreadOriginator(
+            session_configuration.originator.clone(),
+        ));
         let mcp_thread_init = thread_extension_init.clone();
         let thread_extension_data = codex_extension_api::ExtensionData::new_with_init(
             thread_id.to_string(),