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/ext/extension-api/src/lib.rs

@@ -47,6 +47,7 @@ pub use contributors::SkillInvocationInput;
 pub use contributors::SkillInvocationKind;
 pub use contributors::ThreadIdleInput;
 pub use contributors::ThreadLifecycleContributor;
+pub use contributors::ThreadOriginator;
 pub use contributors::ThreadResumeInput;
 pub use contributors::ThreadStartInput;
 pub use contributors::ThreadStopInput;