chore: rename package from @hykocx/zen to @zen/core

Update all references across source files, documentation, and
configuration to reflect the new package scope and name. This includes
updating `.npmrc` registry config, install instructions, module
examples, and all import path comments throughout the codebase.

src/modules/posts/db.js

@@ -3,7 +3,7 @@
  * Creates zen_posts and zen_posts_category tables.
  */
 
-import { query } from '@hykocx/zen/database';
+import { query } from '@zen/core/database';
 import { getPostsConfig } from './config.js';
 
 async function tableExists(tableName) {