feat: add kyberforge plugin and rename plugin-create skill

Scaffolds the kyberforge marketplace management plugin (create-plugin and
marketplace-architect skills will live here). Renames the plugin-create
skill directory to create-plugin to match the canonical kebab-order convention.

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

.github/plugin/marketplace.json

@@ -10,6 +10,11 @@
       "name": "hello-world",
       "description": "A minimal example plugin to validate marketplace scaffolding.",
       "source": "./plugins/hello-world"
+    },
+    {
+      "name": "kyberforge",
+      "description": "Skills and agents for creating, maintaining, and managing a Claude Code / Copilot CLI plugin marketplace.",
+      "source": "./plugins/kyberforge"
     }
   ]
 }