Fix Prometheus and Loki Ingress host matching for ProxyGroup

Remove explicit `host:` field from Ingress rules. With ProxyGroup-based
Tailscale Ingresses, the Host header contains the FQDN (e.g.,
prometheus.tail8d86e.ts.net) which doesn't match the short name
(prometheus), causing 404s.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

argocd/manifests/loki/ingress-tailscale.yaml

@@ -13,8 +13,7 @@ metadata:
 spec:
   ingressClassName: tailscale
   rules:
-    - host: loki
-      http:
+    - http:
         paths:
           - path: /
             pathType: Prefix

argocd/manifests/prometheus/ingress-tailscale.yaml

@@ -19,8 +19,7 @@ metadata:
 spec:
   ingressClassName: tailscale
   rules:
-    - host: prometheus
-      http:
+    - http:
         paths:
           - path: /
             pathType: Prefix