feat(recipes): add NIM Operator recipe for CNCF AI Conformance

[yuanchen8911]

Summary

• Add k8s-nim-operator as a new AICR component for NVIDIA NIM inference platform
• Create H100/EKS/Ubuntu inference recipe for NIM on EKS conformance certification
• Fix health check assert file loading (pre-existing gap affecting all components)

Changes

Recipe & Component:

• Add nim platform type to recipe criteria (pkg/recipe/criteria.go)
• Register k8s-nim-operator v3.1.0 in recipes/registry.yaml with health check, node scheduling paths (operator.nodeSelector, operator.tolerations), and admission controller config
• Create h100-eks-ubuntu-inference-nim.yaml overlay inheriting from h100-eks-ubuntu-inference, adds NIM Operator + DRA support, full conformance validation suite (11 checks)
• Add recipes/components/k8s-nim-operator/values.yaml with correct chart value paths and EKS-compatible affinity

Health Check Fix:

• Load healthCheck.assertFile content into ComponentRef.HealthCheckAsserts in ApplyRegistryDefaults — previously the file path was registered but content was never read, so deployment validation never executed Chainsaw health checks for any component
• Add targeted unit tests for the loading path (success, no-overwrite, missing file)

Demo & Workload:

• Add demos/workloads/inference/nimservice-llama-3-2-1b.yaml — NIMService CR deploying Llama 3.2 1B with NGC secrets, PVC, and GPU tolerations
• Add demos/workloads/inference/nim-chat-server.sh and nim-chat.html — chat UI for testing NIM inference

Test plan

• go test -race ./pkg/recipe/... passes (criteria + health check loading tests)
• aicr recipe --platform nim generates correct 15-component recipe
• aicr bundle generates correct values with operator.tolerations and operator.nodeSelector
• Full deploy on EKS cluster (H100, 6 nodes) — all 15 components deployed successfully
• NIMService CR deploys Llama 3.2 1B, serves /v1/chat/completions
• CNCF conformance validation passes 9/9 checks
• Chat UI works via nim-chat-server.sh

Closes #473