Publish shadcn as a third-party market source

Add shadcn-ui/ui skills/shadcn to the external source registry and generate the public Codex plugin with localized Chinese marketplace metadata. Index the plugin in both marketplace entry points and lock the synced upstream commit.

Constraint: Third-party plugin contents are generated from config/external-sources.json and locked to the upstream commit recorded in external-sources.lock.json.
Rejected: Hand-editing generated shadcn plugin metadata | Localized display fields belong in manifestOverrides and skillDescriptions so future syncs preserve them.
Confidence: high
Scope-risk: narrow
Directive: Re-run the external source sync instead of manually editing plugins/codex/plugins/shadcn when upstream changes.
Tested: python scripts/validate_marketplace.py; python /Users/eapil/.codex/skills/.system/plugin-creator/scripts/validate_plugin.py plugins/codex/plugins/shadcn; git diff --check.
Not-tested: Codex marketplace install/remove smoke test was not run.

.agents/plugins/marketplace.json

@@ -159,6 +159,18 @@
         "authentication": "ON_INSTALL"
       },
       "category": "设计"
+    },
+    {
+      "name": "shadcn",
+      "source": {
+        "source": "local",
+        "path": "./plugins/codex/plugins/shadcn"
+      },
+      "policy": {
+        "installation": "AVAILABLE",
+        "authentication": "ON_INSTALL"
+      },
+      "category": "开发工具"
     }
   ]
 }