Add output schema to MCP tools and expose MCP tool results in code mode (#14236)

Summary
- drop `McpToolOutput` in favor of `CallToolResult`, moving its helpers
to keep MCP tooling focused on the final result shape
- wire the new schema definitions through code mode, context, handlers,
and spec modules so MCP tools serialize the exact output shape expected
by the model
- extend code mode tests to cover multiple MCP call scenarios and ensure
the serialized data matches the new schema
- refresh JS runner helpers and protocol models alongside the schema
changes

Testing
- Not run (not requested)

codex-rs/core/src/tools/js_repl/mod.rs

@@ -622,7 +622,7 @@ impl JsReplManager {
             }
             ResponseInputItem::McpToolCallOutput { output, .. } => {
                 let function_output = output.as_function_call_output_payload();
-                let payload_kind = if output.success {
+                let payload_kind = if output.success() {
                     JsReplToolCallPayloadKind::McpResult
                 } else {
                     JsReplToolCallPayloadKind::McpErrorResult
@@ -634,7 +634,7 @@ impl JsReplManager {
                 );
                 summary.payload_item_count = Some(output.content.len());
                 summary.structured_content_present = Some(output.structured_content.is_some());
-                summary.result_is_error = Some(!output.success);
+                summary.result_is_error = Some(!output.success());
                 summary
             }
         }