Improve marketplace metadata compatibility with official Anthropic schema

Add $schema and top-level description fields to align with the dominant
pattern used in anthropics/claude-code and anthropics/claude-plugins-official.
Existing metadata wrapper preserved for backward compatibility.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -1,5 +1,7 @@
 {
+  "$schema": "https://anthropic.com/claude-code/marketplace.schema.json",
   "name": "android-reverse-engineering-skill",
+  "description": "Claude Code plugins for Android reverse engineering",
   "owner": {
     "name": "Simone Avogadro"
   },