rename: hub-guide -> code-guide

Change plugin name from 'hub-guide' to 'code-guide' to avoid AI
interpreting it as Hub-specific. Skills now show as code-guide:skill-name.
Universal best-practice, not limited to any specific project.

.claude-plugin/plugin.json

@@ -1,5 +1,5 @@
 {
-  "name": "hub-guide",
+  "name": "code-guide",
   "version": "0.2.0",
   "description": "Comprehensive programming best-practice guide for all situations — monorepo, standalone, all languages and frameworks",
   "author": {