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/tools/src/image_detail.rs

@@ -16,7 +16,7 @@ pub fn normalize_output_image_detail(
             Some(ImageDetail::Original)
         }
         Some(ImageDetail::Original) | None => None,
-        Some(ImageDetail::Auto | ImageDetail::Low | ImageDetail::High) => detail,
+        Some(ImageDetail::High) => Some(ImageDetail::High),
     }
 }
 

codex-rs/tools/src/image_detail_tests.rs

@@ -70,10 +70,6 @@ fn explicit_original_is_dropped_without_model_support() {
 fn explicit_non_original_detail_is_preserved() {
     let model_info = model_info();
 
-    assert_eq!(
-        normalize_output_image_detail(&model_info, Some(ImageDetail::Low)),
-        Some(ImageDetail::Low)
-    );
     assert_eq!(
         normalize_output_image_detail(&model_info, Some(ImageDetail::High)),
         Some(ImageDetail::High)
@@ -92,7 +88,7 @@ fn sanitize_original_falls_back_to_high_without_support() {
         },
         FunctionCallOutputContentItem::InputImage {
             image_url: "data:image/png;base64,BBB".to_string(),
-            detail: Some(ImageDetail::Low),
+            detail: Some(ImageDetail::High),
         },
     ];
 
@@ -110,7 +106,7 @@ fn sanitize_original_falls_back_to_high_without_support() {
             },
             FunctionCallOutputContentItem::InputImage {
                 image_url: "data:image/png;base64,BBB".to_string(),
-                detail: Some(ImageDetail::Low),
+                detail: Some(ImageDetail::High),
             },
         ]
     );