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/analytics/src/analytics_client_tests.rs

@@ -279,6 +279,7 @@ fn sample_turn_start_request(thread_id: &str, request_id: i64) -> ClientRequest
                 },
                 UserInput::Image {
                     url: "https://example.com/a.png".to_string(),
+                    detail: None,
                 },
             ],
             ..Default::default()
@@ -399,6 +400,7 @@ fn sample_turn_steer_request(
                 },
                 UserInput::LocalImage {
                     path: "/tmp/a.png".into(),
+                    detail: None,
                 },
             ],
             responsesapi_client_metadata: None,