refactor: 删除已过时的 skill-manager-plugin

功能已被 generate-marketplace.py、claude-config.yaml、sync-skills.sh 完全覆盖。

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

.claude-plugin/marketplace.json

@@ -535,18 +535,6 @@
       ],
       "strict": false
     },
-    {
-      "name": "skill-manager-plugin",
-      "source": "./skills-workflow/skill-manager-plugin",
-      "description": "|",
-      "version": "1.0.0",
-      "category": "utility",
-      "keywords": [
-        "utility",
-        "tools"
-      ],
-      "strict": false
-    },
     {
       "name": "coolbuy-legacy-plugin",
       "source": "./skills-projects/coolbuy-legacy-plugin",