docs(doc-1410): fix vale heading capitalization in batch 4

Apply sentence-style capitalization to four headings flagged by
Google.Headings:
- argocd.mdx: Tenant Cluster Integration, Enable Tenant Cluster Import
- gitlab-ci.mdx: Tenant Clusters for Merge Requests
- karpenter.mdx: Configure Control Plane Cluster Kubernetes RBAC permissions

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

Author: djwfyi

platform/integrations/argocd.mdx

@@ -259,9 +259,9 @@ App Project integration, can be enabled by editing a project manifest and settin
 provide metadata fields to apply the Argo CD App Project object, Argo CD RBAC roles to apply,
 and an array of permissible source repositories that may be accessed within the project.
 
-## Tenant Cluster Integration
+## Tenant cluster integration
 
-### Enable Tenant Cluster Import
+### Enable tenant cluster import
 
 Once a project has Argo CD enabled, tenant clusters within that project are eligible to be
 synced to the Argo instance as available clusters. You can enable tenant cluster import into

platform/integrations/gitlab-ci.mdx

@@ -8,7 +8,7 @@ When using vCluster Platform with GitLab you can use the
 official image `ghcr.io/loft-sh/vcluster-cli` as either a base image or
 directly. If additional tooling is needed for your CI/CD process, a custom image can be created.
 
-## Tenant Clusters for Merge Requests
+## Tenant clusters for merge requests
 
 This example shows how to create and delete a Tenant Cluster for running end-to-end tests for
 the default branch and merge requests. It assumes you have configured CI/CD variables `VCLUSTER_PRO_URL`,

platform/integrations/karpenter.mdx

@@ -154,7 +154,7 @@ kubectl logs -f -n "kube-system" -l app.kubernetes.io/name=karpenter -c controll
   </TabItem>
 </Tabs>
 
-## Configure Control Plane Cluster Kubernetes RBAC permissions
+## Configure control plane cluster Kubernetes RBAC permissions
 
 To deploy the manifests presented in the remainder of this article you will need certain permissions in the Kubernetes control plane cluster. The following Kubernetes permissions will be required in the control plane cluster for the user: