feat(open-webui): deploy Open WebUI with litellm backend

Deploys Open WebUI (chat.k8s.syd1.au.unkin.net) into the open-webui
namespace via the aitooling ArgoCD project. Uses SQLite with a 10Gi
cephrbd PVC for persistence, routes model requests to the existing
litellm deployment, and exposes the UI through the traefik-external
gateway. Credentials (OPENAI_API_KEY, WEBUI_SECRET_KEY) are injected
via VaultStaticSecret from kv/kubernetes/namespace/open-webui/default.

Closes #155

argocd/applicationsets/aitooling.yaml

@@ -11,6 +11,7 @@ spec:
       revision: HEAD
       directories:
       - path: apps/overlays/*/litellm
+      - path: apps/overlays/*/open-webui
       - path: apps/overlays/*/paperclip
   template:
     metadata:

argocd/projects/aitooling.yaml

@@ -11,6 +11,8 @@ spec:
   destinations:
     - namespace: 'litellm'
       server: https://kubernetes.default.svc
+    - namespace: 'open-webui'
+      server: https://kubernetes.default.svc
     - namespace: 'paperclip'
       server: https://kubernetes.default.svc
   clusterResourceWhitelist: