Improve CORS error handling

Add specific error message for CORS-related fetch failures to help users understand when cross-origin requests are blocked.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

index.html

@@ -42,7 +42,11 @@
 						</div>
 					`;
 				} catch (error) {
-					responseDiv.innerHTML = `<div class="error">Error: ${error.message}</div>`;
+					let errorMessage = error.message;
+					if (error.message.includes('Failed to fetch') || error.name === 'TypeError') {
+						errorMessage = `CORS Error: ${error.message}. The server may not allow cross-origin requests from this domain.`;
+					}
+					responseDiv.innerHTML = `<div class="error">Error: ${errorMessage}</div>`;
 				}
 			}
 		</script>