Fix ArgoCD apps app permanent OutOfSync

Remove `group: ""` from ignoreDifferences in tailscale-operator and
tailscale-operator-ringtail — ArgoCD normalizes away the empty string
field, so the live state never matches git.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

argocd/apps/tailscale-operator-ringtail.yaml

@@ -11,8 +11,7 @@ spec:
   project: default
   # Tailscale operator mutates externalName from "placeholder" to actual proxy service
   ignoreDifferences:
-    - group: ""
-      kind: Service
+    - kind: Service
       jsonPointers:
         - /spec/externalName
   source:

argocd/apps/tailscale-operator.yaml

@@ -9,8 +9,7 @@ spec:
   project: default
   # Tailscale operator mutates externalName from "placeholder" to actual proxy service
   ignoreDifferences:
-    - group: ""
-      kind: Service
+    - kind: Service
       jsonPointers:
         - /spec/externalName
   source: