feat(labels): add Domain/Viz and Domain/Data labels for cross-plugin integration

Add new Domain category with 2 labels for domain-specific validation gates:
- Domain/Viz: triggers viz-platform design gates for frontend/visualization work
- Domain/Data: triggers data-platform data gates for data engineering work

Update version to 5.6.0 and document Domain Advisory Pattern feature.

Closes #363

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -6,7 +6,7 @@
   },
   "metadata": {
     "description": "Project management plugins with Gitea and NetBox integrations",
-    "version": "5.5.0"
+    "version": "5.6.0"
   },
   "plugins": [
     {