fix: Correct marketplace.json source path format

Change source from "." to "./" to comply with Claude Code marketplace
schema validation requirement.

Error: plugins.0.source: Invalid input: must start with "./"

🤖 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/marketplace.json

@@ -8,7 +8,7 @@
   "plugins": [
     {
       "name": "n8n-mcp-skills",
-      "source": ".",
+      "source": "./",
       "description": "Complete bundle: 5 expert skills for building flawless n8n workflows using n8n-mcp MCP server. Includes skills for expression syntax, MCP tools usage, workflow patterns, validation, and node configuration.",
       "version": "1.0.0",
       "author": {