fix: Add nixpacks configuration for Astro deployment

dealplustech-astro/node_modules/astro/dist/cli/info/infra/yarn-package-manager.d.ts

@@ -0,0 +1,10 @@
+import type { CommandExecutor } from '../../definitions.js';
+import type { PackageManager } from '../definitions.js';
+export declare class YarnPackageManager implements PackageManager {
+    #private;
+    readonly name: string;
+    constructor({ commandExecutor }: {
+        commandExecutor: CommandExecutor;
+    });
+    getPackageVersion(name: string): Promise<string | undefined>;
+}