Show warning/error if WebGPU is not available

Right now, the WebGPU workloads just fail "silently" on Chrome on Linux for example, since WebGPU is not enabled there by default (it needs a flag, sadly). Let's show some error message in the benchmark page instead (preferably red and big), something (very rough AI sketch):
```js
function checkWebGPUSupport() {
if (!navigator.gpu) {
displayWebGPUError("WebGPU API not found in navigator.");
return;
}

navigator.gpu.requestAdapter()
.then(adapter => {
if (adapter) {
console.log("WebGPU is supported. Adapter:", adapter.name);
// You can proceed with WebGPU initialization here
} else {
displayWebGPUError("No WebGPU adapter available. This might be due to a software rendering list, driver issues, or unsupported hardware.");
}
})
.catch(error => {
console.error("Error requesting WebGPU adapter:", error);
displayWebGPUError("WebGPU is not fully supported or enabled. Check browser settings and hardware acceleration.");
});
}

function displayWebGPUError(message) {
let errorDiv = document.getElementById('webgpu-error');
if (!errorDiv) {
errorDiv = document.createElement('div');
errorDiv.id = 'webgpu-error';
// Append to the body, or a specific container if you have one
document.body.appendChild(errorDiv);
}
errorDiv.textContent = "Error: " + message;
}

// Run the check when the DOM is ready
document.addEventListener('DOMContentLoaded', checkWebGPUSupport);
```

CSS:
```css
#webgpu-error {
color: #D93025; /* Google Red 600 */
background-color: #FAD2CF; /* Google Red 50 */
border: 1px solid #C5221F; /* Google Red 700 */
padding: 12px 16px;
margin: 16px 0;
border-radius: 4px;
font-weight: bold;
text-align: center;
}
```

Start by locating the benchmark page's WebGPU initialization and the existing page styling. Check for a missing navigator.gpu, unavailable adapter, and initialization failure, then show a prominent red warning instead of failing silently. Verify the message by opening the benchmark in Chrome on Linux with WebGPU disabled.

Written by the indexing model from the issue text.