Add React API (#39)

* Add React module documentation and update external link styling

* Tweak order

---------

Co-authored-by: Will Eastcott <will@playcanvas.com>

Author: marklundin

index.html

@@ -620,11 +620,17 @@
             border-radius: 4px;
             transition: background-color 0.2s;
             margin-right: 8px;
-            width: 145px;
+            min-width: 145px;
             text-align: center;
             margin-bottom: 8px;
         }
 
+        .module-link.external::after {
+            content: ' ↗';
+            padding-left: 8px;
+            vertical-align: middle;
+        }
+
         .module-link.legacy {
             background-color: rgba(77, 166, 255, 0.3);
             color: rgba(255, 255, 255, 0.8);
@@ -786,20 +792,20 @@ <h3>📖 Engine</h3>
                                 <a href="./engine/" class="module-link">v2.x API (current)</a>
                                 <a href="./engine-v1/" class="module-link legacy">v1.x API (legacy)</a>
                             </li>
-                            <li class="module-item" data-name="web-components">
-                                <h3>📖 Web Components</h3>
-                                <p>Custom HTML elements for building declarative PlayCanvas applications.</p>
-                                <a href="./web-components/" class="module-link">View API Reference</a>
-                            </li>
                             <li class="module-item" data-name="editor">
                                 <h3>📖 Editor</h3>
                                 <p>API for interfacing with the PlayCanvas Editor.</p>
                                 <a href="./editor/" class="module-link">View API Reference</a>
                             </li>
-                            <li class="module-item" data-name="observer">
-                                <h3>📖 Observer</h3>
-                                <p>Reactive data observation and binding system.</p>
-                                <a href="./observer/" class="module-link">View API Reference</a>
+                            <li class="module-item" data-name="react">
+                                <h3>📖 React</h3>
+                                <p>Use React’s declarative power to build PlayCanvas apps with components, hooks, and JSX.</p>
+                                <a href="https://playcanvas-react.vercel.app/docs/api" class="module-link external">View API Reference</a>
+                            </li>
+                            <li class="module-item" data-name="web-components">
+                                <h3>📖 Web Components</h3>
+                                <p>Custom HTML elements for building declarative PlayCanvas applications.</p>
+                                <a href="./web-components/" class="module-link">View API Reference</a>
                             </li>
                             <li class="module-item" data-name="pcui">
                                 <h3>📖 PCUI</h3>
@@ -811,6 +817,11 @@ <h3>📖 PCUI Graph</h3>
                                 <p>Graph user interface components for creating node-based editors.</p>
                                 <a href="./pcui-graph/" class="module-link">View API Reference</a>
                             </li>
+                            <li class="module-item" data-name="observer">
+                                <h3>📖 Observer</h3>
+                                <p>Reactive data observation and binding system.</p>
+                                <a href="./observer/" class="module-link">View API Reference</a>
+                            </li>
                         </ul>
                     </section>
                 </div>
@@ -889,4 +900,4 @@ <h3>📖 PCUI Graph</h3>
         });
     </script>
 </body>
-</html> 
+</html>