Remove hardcoded static values from addon charts

**Parent:** #584
**Priority:** High

Several addon charts contain hardcoded values (`peeks`, `us-west-2`, `system-peeks`) that should be parameterized.

| File | Value | Fix |
|------|-------|-----|
| `devlake/templates/external-secret.yaml` | `peeks-devlake/mysql-connection` | Use `{{ .Values.global.clusterName }}-devlake/mysql-connection` |
| `grafana-dashboards/templates/external-secret.yaml` | `peeks-devlake/mysql-connection` | Same |
| `backstage/templates/install.yaml` | `karpenter.sh/nodepool: system-peeks` | Parameterize via `global.clusterName` |
| `platform-manifests/templates/huggingface-models.yaml` | `default "peeks"`, `default "peeks-hub"` | Remove hardcoded defaults |
| `platform-manifests/templates/ray-system-iamroleselectors.yaml` | `peeks-cluster-mgmt-*` | Use `{{ .Values.global.clusterName }}-cluster-mgmt-*` |
| `ray-operator/templates/model-prestage-job.yaml` | `peeks-ray-models` | Use clusterName-based default |
| `kro/resource-groups/manifests/appmod-service.yaml` | `peeks-cluster-mgmt-*`, `peeks/platform/amp` | Parameterize via schema |
| `kro/resource-groups/manifests/ray-service/ray-service.yaml` | `peeks-ray-models`, `us-west-2` | Use schema fields |
| `grafana/templates/datasources.yaml` | `default "us-west-2"` | Use `{{ .Values.aws.region }}` |
| `keycloak/templates/keycloak-config.yaml` | `s3.us-west-2.amazonaws.com`, kubectl 1.32.0 | Parameterize region and version |
| `addons/configs/image-prepuller/values.yaml` | `general-purpose-peeks` | Parameterize nodepool name |

**Acceptance criteria:**
- No `peeks` string in any template outside KRO schema defaults
- No hardcoded `us-west-2` in templates
- All nodepool references are parameterized

Start by searching the listed addon chart templates, values.yaml, and KRO manifests for `peeks` and `us-west-2`, then review the existing `global.clusterName`, AWS region, and schema fields they expose. The work is done when the acceptance criteria pass: no forbidden hardcoded values remain in templates and all nodepool references are parameterized.

Written by the indexing model from the issue text.