fix: Change repository field from object to string in plugin.json

Claude Code expects repository field to be a string, not an object.

Error: repository: Expected string, received object

Changed from:
"repository": { "type": "git", "url": "..." }

To:
"repository": "https://github.com/czlonkowski/n8n-skills"

This follows Claude Code's plugin.json schema where repository is a simple
string URL rather than npm's package.json format.

Distribution package regenerated with corrected plugin.json.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

.claude-plugin/plugin.json

@@ -15,9 +15,6 @@
     "validation",
     "expressions"
   ],
-  "repository": {
-    "type": "git",
-    "url": "https://github.com/czlonkowski/n8n-skills"
-  },
+  "repository": "https://github.com/czlonkowski/n8n-skills",
   "homepage": "https://github.com/czlonkowski/n8n-skills"
 }