Phase 8: add the Reference App wiki walkthrough (06_reference_app)

- four pages walking the vet sample: overview, domain & API, pipelines &
  worker, spec-driven client admin
- mkdocs nav section, index + start-an-app cross links
- bundle now exposes the walkthrough as wiki_reference_app_* modules

standards/mcp/nav.json

@@ -114,6 +114,26 @@
     "resource": "docs://modules/wiki_mcp_setup",
     "title": "🔌 MCP Setup"
   },
+  {
+    "module": "wiki_reference_app_overview",
+    "resource": "docs://modules/wiki_reference_app_overview",
+    "title": "Overview"
+  },
+  {
+    "module": "wiki_reference_app_domain_and_api",
+    "resource": "docs://modules/wiki_reference_app_domain_and_api",
+    "title": "Domain And Api"
+  },
+  {
+    "module": "wiki_reference_app_pipelines_and_worker",
+    "resource": "docs://modules/wiki_reference_app_pipelines_and_worker",
+    "title": "Pipelines And Worker"
+  },
+  {
+    "module": "wiki_reference_app_client_admin",
+    "resource": "docs://modules/wiki_reference_app_client_admin",
+    "title": "Client Admin"
+  },
   {
     "module": "wiki_index",
     "resource": "docs://modules/wiki_index",