Create dedicated EKS Auto Mode nodepools for addons

**Parent:** #584
**Priority:** Medium

EKS Auto Mode uses a default nodepool for all workloads. Create dedicated nodepools for platform addons to:
- Isolate platform workloads from application workloads
- Set resource limits and instance types per addon category
- Support GPU nodepools for ML/AI addons
- Allow cost attribution per nodepool

Implementation:
- Add nodepool definitions to the PlatformCluster composition or as separate Crossplane resources
- Configure addon charts to use `nodeSelector` or `nodeAffinity` targeting the dedicated nodepool
- Parameterize nodepool name via `global.clusterName` (e.g., `system-{clusterName}`)

Start with the PlatformCluster composition or the separate Crossplane resources, then inspect the addon charts and their global.clusterName values. Done means dedicated nodepools cover the platform addon categories, addon scheduling targets them, and the configuration supports resource and instance settings, GPU workloads, and cost attribution.

Written by the indexing model from the issue text.