test(authz): end-to-end integration coverage, worked example, and docs

Task 15 of the authz permissions plan: proves db store + cache + catalog +
middleware + audit compose correctly, wires a real (non-dangling) example
into auth-showcase, and documents the declaration/registration/precedence
surface in the package README.

examples/auth-showcase/package.json

@@ -12,6 +12,7 @@
   },
   "dependencies": {
     "@wrnexus/auth": "workspace:*",
+    "@wrnexus/authz": "workspace:*",
     "@wrnexus/captcha": "workspace:*",
     "@wrnexus/core": "workspace:*",
     "@wrnexus/validation": "workspace:*"