Force npm install to include devDependencies for generated project builds

lib/validator.ts

@@ -92,7 +92,7 @@ export async function validateProject(
   // Step 1: npm install
   const installResult = await runCommand(
     "npm",
-    ["install", "--no-audit", "--no-fund", "--loglevel=error"],
+    ["install", "--no-audit", "--no-fund", "--loglevel=error", "--include=dev"],
     projectDir,
     installTimeout
   );