Preserve image detail in app-server inputs (#20693)

## Summary

- Add optional image detail to user image inputs across core, app-server
v2, thread history/event mapping, and the generated app-server
schemas/types.
- Preserve requested detail when serializing Responses image inputs:
omitted detail stays on the existing `high` default, while explicit
`original` keeps local images on the original-resolution path.
- Support `high`/`original` consistently for tool image outputs,
including MCP `codex/imageDetail`, code-mode image helpers, and
`view_image`.

codex-rs/core/src/tools/code_mode/response_adapter.rs

@@ -17,8 +17,6 @@ impl IntoProtocol<ImageDetail> for CodeModeImageDetail {
     fn into_protocol(self) -> ImageDetail {
         let value = self;
         match value {
-            CodeModeImageDetail::Auto => ImageDetail::Auto,
-            CodeModeImageDetail::Low => ImageDetail::Low,
             CodeModeImageDetail::High => ImageDetail::High,
             CodeModeImageDetail::Original => ImageDetail::Original,
         }