Support original-detail metadata on MCP image outputs (#17714)

## Summary
- honor `_meta["codex/imageDetail"] == "original"` on MCP image content
and map it to `detail: "original"` where supported
- strip that detail back out when the active model does not support
original-detail image inputs
- update code-mode `image(...)` to accept individual MCP image blocks
- teach `js_repl` / `codex.emitImage(...)` to preserve the same hint
from raw MCP image outputs
- document the new `_meta` contract and add generic RMCP-backed coverage
across protocol, core, code-mode, and js_repl paths

codex-rs/tools/src/lib.rs

@@ -53,6 +53,7 @@ pub use codex_protocol::ToolName;
 pub use dynamic_tool::parse_dynamic_tool;
 pub use image_detail::can_request_original_image_detail;
 pub use image_detail::normalize_output_image_detail;
+pub use image_detail::sanitize_original_image_detail;
 pub use js_repl_tool::create_js_repl_reset_tool;
 pub use js_repl_tool::create_js_repl_tool;
 pub use json_schema::AdditionalProperties;