docs(plan-export): add artifacts directory creation to export example

[Copilot]

Export-IdlePlan throws DirectoryNotFoundException if the output directory doesn't exist, but the documented example silently assumes ./artifacts is present. Also confirms tab indentation was already resolved in a prior commit.

Changes

• docs/use/plan-export.md: Adds New-Item -ItemType Directory -Force -Path ./artifacts | Out-Null before Export-IdlePlan so the example is self-contained and safe to run in a fresh checkout or CI workspace.

$plan = New-IdlePlan -WorkflowPath ./workflows/joiner.psd1 -Request $request

# Create the output directory if it does not already exist
New-Item -ItemType Directory -Force -Path ./artifacts | Out-Null

Export-IdlePlan -Plan $plan -Path ./artifacts/plan.json

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[github-actions]

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[chatgpt-codex-connector]

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