xint-data-dir-writes-inside-releases-not-persistent

xint writes runtime data (api-costs.json, reliability-metrics.json) to a release-internal data/ directory by default, not to the persistent /opt/infra/xint/data/ path. This means all cost tracking and reliability metrics are wiped on every version upgrade. Fix: symlink releases//data → /opt/infra/xint/data/ immediately after install.