platform: networking: null aborts the render at apps.yaml:140 #4072

Describe the bug
packages/core/platform/templates/apps.yaml:140 reads .Values.networking.clusterDomain directly; line 139 above it reads .Values.monitoring through dig. A platform values file with networking: null (Helm deletes the key instead of falling back to the chart default) aborts the whole platform render with a nil pointer at that line.

Environment

• Cozystack main, 2026-09-04 (the line dates from 2d022e3, 2026-01-15)

To Reproduce

1. helm template packages/core/platform --set-json 'networking=null'
2. Nil pointer at apps.yaml:140

Expected behaviour
The render falls back to the chart default, as the neighbouring line does for monitoring.

Actual behaviour
The whole platform render fails. A scoped helm-unittest suite renders only its own templates, so no package suite catches it.

Checklist

• I have checked the documentation
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• I have provided clear steps to reproduce
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