feat: show draft posts/products on testing and staging

- Add config.showDrafts (true for dev/testing/staging, false for production)
- Replace all isDev checks in blog.ts and products.ts with config.showDrafts
- Previously only NODE_ENV=development showed drafts, missing testing/staging

lib/config.ts

@@ -29,6 +29,7 @@ function createConfig() {
     isStaging: target === 'staging',
     isTesting: target === 'testing',
     isDevelopment: target === 'development',
+    showDrafts: target === 'development' || target === 'testing' || target === 'staging',
     feedbackEnabled: env.NEXT_PUBLIC_FEEDBACK_ENABLED,
     gatekeeperUrl: env.GATEKEEPER_URL,
 
@@ -116,6 +117,9 @@ export const config = {
   get isDevelopment() {
     return getConfig().isDevelopment;
   },
+  get showDrafts() {
+    return getConfig().showDrafts;
+  },
   get baseUrl() {
     return getConfig().baseUrl;
   },