fix: pass explicit platform to krane export to fix arm64 skill loading

[iplay88keys]

Description

Fixes #1486

• krane export defaults to linux/amd64 when resolving multi-platform OCI image indexes, regardless of the actual node architecture
• On arm64 nodes, skills-init crashes with no child with platform linux/amd64 in index <image>, putting the pod in CrashLoopBackOff and preventing the agent from becoming Ready
• Fix detects the node architecture at runtime via uname -m and passes it explicitly to krane via --platform

Testing

• Deployed on arm64 kind cluster (Apple Silicon) — TestE2EInvokeSkillInAgent passes
• All E2E tests pass

[Copilot]

Pull request overview

Fixes arm64 agent startup failures by ensuring skills-init pulls the correct architecture variant from multi-platform OCI image indexes when running krane export.

Changes:

• Detect node CPU architecture at runtime via uname -m (normalized to OCI arch strings).
• Pass an explicit --platform linux/<arch> to krane export to avoid defaulting to linux/amd64.

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[Copilot]

The arch normalization uses a uname -m | sed ... pipeline with substring replacements. This can produce invalid platforms for values that contain those substrings (e.g. aarch64_be -> arm64_be) and makes it hard to fail fast on unsupported architectures. Consider switching to an explicit case mapping (x86_64/amd64 -> amd64, aarch64/arm64 -> arm64) and exiting with a clear error for anything else before invoking krane.

Suggested change

	_arch="$(uname -m | sed 's/x86_64/amd64/;s/aarch64/arm64/')"
	_uname="$(uname -m)"
	case "$_uname" in
	x86_64|amd64)
	_arch="amd64"
	;;
	aarch64|arm64)
	_arch="arm64"
	;;
	*)
	echo "Unsupported architecture for OCI export: ${_uname}" >&2
	exit 1
	;;
	esac

[iplay88keys]

Works for me 👍