refactor(kro): convert resource-groups manifests to a Helm chart for value injection

## Problem

The KRO ResourceGraphDefinitions in `gitops/addons/charts/kro/resource-groups/manifests/` are deployed by ArgoCD in **directory mode** (`type: manifest` + `directory.recurse: true`), not as a Helm chart.

Registry entries (`kro-manifests`, `kro-manifests-hub`):
```yaml
kro-manifests-hub:
type: manifest
path: ...addons/charts/kro/resource-groups/manifests
directory:
recurse: true
```

Because there is no Helm templating, the RGDs rely on **hardcoded KRO schema defaults** and cannot receive cluster-specific values from the cluster secret annotations.

## Symptoms

- `deployClusterName: string | default="peeks-spoke-dev"` — wrong default; spoke cluster names are `spoke-dev`/`spoke-prod` on this branch
- `resourcePrefix: string | default="peeks"` — hardcoded
- `peeks-cluster-mgmt-*` role names hardcoded in IAMRoleSelectors
- ECR repo paths hardcode `peeks/` prefix

Workaround currently applied: inject the missing values via the Backstage `system-info` entity (e.g. `spoke_dev_cluster_name`, `spoke_prod_cluster_name`) and map them in the templates/skeletons. This works for Backstage-driven flows but does not fix the RGD defaults themselves.

## Proposed Solution

Convert `addons/charts/kro/resource-groups/` into a proper Helm chart:

1. Add `Chart.yaml` + `values.yaml`
2. Template the RGD schema defaults and IAMRoleSelector ARNs from values:
- `clusterName`, `resourcePrefix`, `accountId`, `region`
- spoke cluster names (`deployClusterName`)
- `{prefix}-cluster-mgmt-*` role names
3. Change the registry entries from `type: manifest`/`directory` to Helm with `valuesObject` sourced from cluster secret annotations (same pattern as other addons):
```yaml
valuesObject:
global:
clusterName: "{{.metadata.annotations.aws_cluster_name}}"
resourcePrefix: "{{.metadata.annotations.resource_prefix}}"
accountId: "{{.metadata.annotations.aws_account_id}}"
region: "{{.metadata.annotations.aws_region}}"
```

## Impact

- Removes hardcoded `peeks*` defaults
- Per-environment / per-cluster RGD customization
- Consistent with the rest of the addon registry (Helm-based)
- Enables proper multi-account / multi-cluster naming

## Scope

Affects: `deployClusterName`, `resourcePrefix`, mgmt role names, ECR prefixes across appmodservice, cicd-pipeline, ray-service, eks RGDs.

## References

- PR #709
- Related: #714 (AppmodService resources field)

Start with addons/charts/kro/resource-groups/manifests/ and the registry entries for kro-manifests and kro-manifests-hub; compare them with other Helm-based addons. Trace the appmodservice, cicd-pipeline, ray-service, and eks RGDs to identify every hardcoded default and selector. Done means the directory is a Helm chart, registry values come from cluster annotations, and the affected names and prefixes are configurable per cluster.

Written by the indexing model from the issue text.