postiz: bump memory request 512Mi → 2Gi, limit 4Gi → 3Gi (right-size for next deploy)

krr 2026-05-22 flagged postiz-app as critically under-requested when it
was running (gap 2.2 GiB above the 512Mi request). Postiz is currently
uninstalled in the cluster — this change is only for when the stack is
re-deployed later. No apply triggered now.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

stacks/postiz/modules/postiz/main.tf

@@ -207,10 +207,10 @@ resource "helm_release" "postiz" {
     resources = {
       requests = {
         cpu    = "100m"
-        memory = "512Mi"
+        memory = "2Gi"
       }
       limits = {
-        memory = "4Gi"
+        memory = "3Gi"
       }
     }