Update CLUSTER-BUILD.md to reflect the current state of the Talos cluster, detailing progress through Phase D (observability) and advancements in Phase E (secrets). Include updates on Sealed Secrets, External Secrets Operator, and Vault configurations, along with deployment instructions and next steps for Kubernetes auth and ClusterSecretStore integration. Mark relevant tasks as completed and outline remaining objectives for future phases.

clusters/noble/apps/sealed-secrets/README.md

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+# Sealed Secrets (noble)
+
+Encrypts `Secret` manifests so they can live in git; the controller decrypts **SealedSecret** resources into **Secret**s in-cluster.
+
+- **Chart:** `sealed-secrets/sealed-secrets` **2.18.4** (app **0.36.1**)
+- **Namespace:** `sealed-secrets`
+
+## Install
+
+```bash
+helm repo add sealed-secrets https://bitnami-labs.github.io/sealed-secrets
+helm repo update
+kubectl apply -f clusters/noble/apps/sealed-secrets/namespace.yaml
+helm upgrade --install sealed-secrets sealed-secrets/sealed-secrets -n sealed-secrets \
+  --version 2.18.4 -f clusters/noble/apps/sealed-secrets/values.yaml --wait
+```
+
+## Workstation: `kubeseal`
+
+Install a **kubeseal** build compatible with the controller (match **app** minor, e.g. **0.36.x** for **0.36.1**). Examples:
+
+- **Homebrew:** `brew install kubeseal` (check `kubeseal --version` against the chart’s `image.tag` in `helm show values`).
+- **GitHub releases:** [bitnami-labs/sealed-secrets](https://github.com/bitnami-labs/sealed-secrets/releases)
+
+Fetch the cluster’s public seal cert (once per kube context):
+
+```bash
+kubeseal --fetch-cert > /tmp/noble-sealed-secrets.pem
+```
+
+Create a sealed secret from a normal secret manifest:
+
+```bash
+kubectl create secret generic example --from-literal=foo=bar --dry-run=client -o yaml \
+  | kubeseal --cert /tmp/noble-sealed-secrets.pem -o yaml > example-sealedsecret.yaml
+```
+
+Commit `example-sealedsecret.yaml`; apply it with `kubectl apply -f`. The controller creates the **Secret** in the same namespace as the **SealedSecret**.
+
+## Backup the sealing key
+
+If the controller’s private key is lost, existing sealed files cannot be decrypted on a new cluster. Back up the key secret after install:
+
+```bash
+kubectl get secret -n sealed-secrets -l sealedsecrets.bitnami.com/sealed-secrets-key=active -o yaml > sealed-secrets-key-backup.yaml
+```
+
+Store `sealed-secrets-key-backup.yaml` in a safe offline location (not in public git).