Publish third-party presentation skills

Add frontend-slides, guizang-ppt-skill, html-ppt, and ppt-master as public third-party marketplace sources with localized Chinese metadata, provenance locks, and generated Codex plugin directories. The sync script now handles root-directory skills without VCS/cache artifacts and supports sparse checkout for large upstream repositories.

Constraint: Third-party plugin content is generated from config/external-sources.json and locked to the upstream commit recorded in external-sources.lock.json.
Rejected: Keeping administrator-added local copies | Stable third-party sources give clearer provenance and let KeyInfo replace duplicates consistently.
Confidence: high
Scope-risk: moderate
Directive: Re-run external source sync instead of manually editing generated plugin directories; keep ppt-master sparseCheckout scoped unless the upstream skill layout changes.
Tested: python scripts/validate_marketplace.py; python /Users/eapil/.codex/skills/.system/plugin-creator/scripts/validate_plugin.py plugins/codex/plugins/frontend-slides; python /Users/eapil/.codex/skills/.system/plugin-creator/scripts/validate_plugin.py plugins/codex/plugins/guizang-ppt-skill; python /Users/eapil/.codex/skills/.system/plugin-creator/scripts/validate_plugin.py plugins/codex/plugins/html-ppt; python /Users/eapil/.codex/skills/.system/plugin-creator/scripts/validate_plugin.py plugins/codex/plugins/ppt-master; git diff --check.
Not-tested: Codex marketplace install/remove smoke test and PowerShell sync execution were not run; pwsh/powershell is unavailable on this machine.

plugins/codex/.agents/plugins/marketplace.json

@@ -171,6 +171,54 @@
         "authentication": "ON_INSTALL"
       },
       "category": "开发工具"
+    },
+    {
+      "name": "frontend-slides",
+      "source": {
+        "source": "local",
+        "path": "./plugins/frontend-slides"
+      },
+      "policy": {
+        "installation": "AVAILABLE",
+        "authentication": "ON_INSTALL"
+      },
+      "category": "文档处理"
+    },
+    {
+      "name": "guizang-ppt-skill",
+      "source": {
+        "source": "local",
+        "path": "./plugins/guizang-ppt-skill"
+      },
+      "policy": {
+        "installation": "AVAILABLE",
+        "authentication": "ON_INSTALL"
+      },
+      "category": "文档处理"
+    },
+    {
+      "name": "html-ppt",
+      "source": {
+        "source": "local",
+        "path": "./plugins/html-ppt"
+      },
+      "policy": {
+        "installation": "AVAILABLE",
+        "authentication": "ON_INSTALL"
+      },
+      "category": "文档处理"
+    },
+    {
+      "name": "ppt-master",
+      "source": {
+        "source": "local",
+        "path": "./plugins/ppt-master"
+      },
+      "policy": {
+        "installation": "AVAILABLE",
+        "authentication": "ON_INSTALL"
+      },
+      "category": "文档处理"
     }
   ]
 }