Add local glTF viewer and visual coverage

Amp-Thread-ID: https://ampcode.com/threads/T-01a02d1c-27fc-7761-9f51-ed97b2dd4e3e
Co-authored-by: Heaust Azure <heaust.azure@gmail.com>

server/web/gltf.html

@@ -0,0 +1,47 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1" />
+    <meta name="theme-color" content="#06111d" />
+    <meta
+      name="description"
+      content="Open a local glTF or GLB file in the Yawn WebGPU viewer."
+    />
+    <title>glTF Viewer — Yawn</title>
+    <link rel="stylesheet" href="/assets/gltf.css" />
+    <script type="importmap">
+      {
+        "imports": {
+          "@yawn/core": "/pkg/core.js",
+          "@yawn/handles": "/pkg/handles.js"
+        }
+      }
+    </script>
+    <script type="module" src="/assets/gltf.js"></script>
+  </head>
+  <body>
+    <main id="drop-zone" class="viewer" aria-label="Yawn glTF viewer">
+      <canvas id="canvas" aria-label="3D model preview"></canvas>
+
+      <output id="render-time" class="render-time" hidden>
+        <span>Render</span>
+        <strong id="render-value">— ms</strong>
+      </output>
+
+      <button id="drop-prompt" class="drop-prompt" type="button">
+        <span class="drop-icon" aria-hidden="true">↓</span>
+        <strong id="prompt-message">Drop a glTF file</strong>
+        <small id="prompt-detail"
+          >GLB or self-contained glTF · processed locally</small
+        >
+      </button>
+      <input
+        id="file-picker"
+        type="file"
+        accept=".glb,.gltf,model/gltf-binary,model/gltf+json"
+        hidden
+      />
+    </main>
+  </body>
+</html>