feat: add halcon skill v2 plugin + fix marketplace source paths

- plugins/halcon: MVTec HALCON machine-vision skill v2 (local Windows HALCON
  + remote halcon-remote MCP). Bundles 2387-operator index, 20 official 24.11
  manuals, HDevEngine runners, ROI teaching, D2W overlay recipes.
- marketplace.json: register halcon; switch both entries to ./plugins/<name>
  source form (bare-name+pluginRoot was rejected by claude plugin validate
  v2.1.202); drop now-unused metadata.pluginRoot.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -4,14 +4,16 @@
     "name": "goldyard"
   },
   "description": "Totoro 归墟 Claude Code skills marketplace",
-  "metadata": {
-    "pluginRoot": "./plugins"
-  },
   "plugins": [
     {
       "name": "hello-skill",
-      "source": "hello-skill",
+      "source": "./plugins/hello-skill",
       "description": "示例技能插件,验证市场可安装"
+    },
+    {
+      "name": "halcon",
+      "source": "./plugins/halcon",
+      "description": "MVTec HALCON 机器视觉 skill(v2):本地 Windows HALCON 或远程 halcon-remote MCP(无需本地安装)。找圆/拟合/1D-2D-3D 量测/匹配/标定/条码数据码/OCR/D2W 套圈对位;含 2387 算子索引 + 20 本官方 24.11 手册。"
     }
   ]
 }