build: use node-modules linker so plain jlpm works

Removes the pnpm node-linker so 'jlpm test' / 'jlpm build' run directly
without the YARN_NODE_LINKER=node-modules env override. Re-run 'jlpm
install' to regenerate node_modules in the flat layout (the in-flight
yarn.lock migration in package.json already targets node-modules).

.yarnrc.yml

@@ -4,7 +4,7 @@ enableGlobalCache: false
 
 enableScripts: false
 
-nodeLinker: pnpm
+nodeLinker: node-modules
 
 packageExtensions:
   "@module-federation/sdk@*":