fix: correct marketplace.json source field format

Change source from absolute GitHub URL to relative path "./"
This follows Claude Code marketplace convention where source paths
are relative to the cloned repository root, not external URLs.

Matches pattern from working examples like claude-homelab marketplace.

.claude-plugin/marketplace.json

@@ -13,7 +13,7 @@
   "plugins": [
     {
       "name": "unraid",
-      "source": "https://github.com/jmagar/unraid-mcp",
+      "source": "./",
       "description": "Query and monitor Unraid servers via GraphQL API - array status, disk health, containers, VMs, system monitoring",
       "version": "0.2.0",
       "tags": ["unraid", "monitoring", "homelab", "graphql", "docker", "virtualization"],