fix: preserve structured McpError data in request history

When a tool call returns an MCP error (e.g. -32042 URLElicitationRequired),
the catch block was only capturing error.message (a string), discarding the
structured error.code and error.data fields.

Now McpError instances push the full JSON-RPC error structure to history:
  { error: { code, message, data } }

This means the Response panel will show the complete error including
data.elicitations for -32042, rather than just a message string.

Author: evalstate

client/src/lib/hooks/useConnection.ts

@@ -259,9 +259,19 @@ export function useConnection({
 
         pushHistory(requestWithMetadata, response);
       } catch (error) {
-        const errorMessage =
-          error instanceof Error ? error.message : String(error);
-        pushHistory(requestWithMetadata, { error: errorMessage });
+        if (error instanceof McpError) {
+          pushHistory(requestWithMetadata, {
+            error: {
+              code: error.code,
+              message: error.rpcMessage ?? error.message,
+              ...(error.data !== undefined && { data: error.data }),
+            },
+          });
+        } else {
+          const errorMessage =
+            error instanceof Error ? error.message : String(error);
+          pushHistory(requestWithMetadata, { error: errorMessage });
+        }
         throw error;
       }