feat: generate .assetsignore file for Cloudflare deployment

.changeset/proud-taxis-admire.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-cloudflare': minor
+---
+
+feat: add `.assetsignore` file to avoid serving known server-only files to browser

packages/adapter-cloudflare/index.js

@@ -143,6 +143,8 @@ export default function (options = {}) {
 					}`
 				);
 			}
+
+			writeFileSync(`${dest}/.assetsignore`, generate_assetsignore(), { flag: 'a' });
 		},
 		async emulate() {
 			const proxy = await getPlatformProxy(options.platformProxy);
@@ -263,3 +265,13 @@ ${rules}
 # === END AUTOGENERATED SVELTE PRERENDERED REDIRECTS ===
 `.trimEnd();
 }
+
+function generate_assetsignore() {
+	// this comes from https://github.com/cloudflare/workers-sdk/blob/main/packages/create-cloudflare/templates-experimental/svelte/templates/static/.assetsignore
+	return `
+_worker.js
+_routes.json
+_headers
+_redirects
+`;
+}