wiki: client Wi-Fi inventory structure (vault-backed) + memory; ignore .ocu scratch

- wiki/reference/client-wifi.md: readable index (no passwords), /wiki-compile-exempt
- reference_client_wifi_inventory.md: convention (vault clients/<slug>/wifi.sops.yaml)
- wiki/index.md: new Reference section
- .gitignore: .ocu.* scratch artifacts

.gitignore

@@ -147,3 +147,6 @@ temp/
 .one.json
 .rmm-token
 .rmm-url
+
+# Scratch output from ocu/openclaw tooling (empty error/json artifacts)
+.ocu.*