fix: avoid Helm archive check pipe failure

[pierinho13]

Summary

• write the complete Helm archive listing to a temporary file
• check values.schema.json without an early-closing grep pipeline
• avoid tar SIGPIPE failures under set -o pipefail

The chart signature and schema were already valid in the failed run; this fixes only the false-negative verification step.

Validation

• package snapshot chart
• run the archive check with set -euo pipefail
• git diff --check
• repository pre-commit hooks