Sync third-party and MCP marketplace plugins

Constraint: Public skills are published only by explicit administrator action unless they are tracked third-party market sources.
Confidence: high
Scope-risk: narrow
Directive: Keep private/internal skills out of the public marketplace and preserve normal incremental market Git history.
Tested: Marketplace validation passed.

config/external-sources.lock.json

@@ -33,8 +33,8 @@
       "repo": "https://github.com/shadcn-ui/ui.git",
       "ref": "main",
       "adapter": "claude-skill",
-      "commit": "c879483c9694d7b135ed1efe8f73233d924ae551",
-      "syncedAt": "2026-06-17T07:05:29Z"
+      "commit": "c2ddedf5d24e0cee05936c69e1f199a9975a07b2",
+      "syncedAt": "2026-06-18T16:00:00Z"
     },
     {
       "id": "frontend-slides",
@@ -69,8 +69,8 @@
       "repo": "https://github.com/hugohe3/ppt-master.git",
       "ref": "main",
       "adapter": "claude-skill",
-      "commit": "313ee6729dba50cbdd50b67debe601c483a5bcab",
-      "syncedAt": "2026-06-17T07:05:29Z"
+      "commit": "7249902c363f0b33dee9a9f7112fb258ae9c3bf7",
+      "syncedAt": "2026-06-18T16:00:00Z"
     },
     {
       "id": "next-skills",