Cache path moved from /tmp/.foxhunt_imbalance_cache/ (ephemeral,
lost between Argo pods) to <mbp10_dir>/.cache/ (on the training-data
PVC). Saves ~4 minutes per Argo submission by avoiding recomputation
of 209M trade ticks → 17.8M imbalance bars.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>