webui: make input box focus on page load

Add a window.load event listener in the firstUpdated lifecycle method to ensure
the chat input gets focused when the page loads completely.

Co-Authored-By: sketch <hello@sketch.dev>
diff --git a/webui/src/web-components/sketch-chat-input.ts b/webui/src/web-components/sketch-chat-input.ts
index 257c583..fb273bc 100644
--- a/webui/src/web-components/sketch-chat-input.ts
+++ b/webui/src/web-components/sketch-chat-input.ts
@@ -141,6 +141,17 @@
       // Initialize the input height
       this.adjustChatSpacing();
     }
+
+    // Add window.onload handler to ensure the input is focused when the page fully loads
+    window.addEventListener(
+      "load",
+      () => {
+        if (this.chatInput) {
+          this.chatInput.focus();
+        }
+      },
+      { once: true },
+    );
   }
 
   render() {