feat: add a modern design for the result image

The shared result image had one look, and it no longer matched the modern
frontend.

The renderer can now draw either design. The image follows the same
useNewDesign setting as the frontend, so a deployment has one switch rather
than two that can disagree, and classic remains the fallback.

- An explicit style query parameter overrides it, which is how the modern
  frontend asks for the design it matches.

- The modern design reuses the frontend palette and shows the client, address
  family and timestamp already present in the result data.

frontend/javascript/index.js

@@ -419,7 +419,10 @@ function startRenderingLoop() {
             window.location.href.lastIndexOf("/")
           ) +
           "/results/?id=" +
-          testState.testData.testId;
+          testState.testData.testId +
+          // Ask for the design this frontend matches; the classic frontend
+          // links the same URL and gets the classic image without asking.
+          "&style=modern";
       }
 
       testState.testDataDirty = false;