xint-runtime-data-writes-to-release-internal-dir-by-default

xint writes runtime data (api-costs.json, reliability-metrics.json) to its own release-internal data/ directory by default, not any externally configured persistent path. Without intervention, this data is wiped on every version upgrade. Fix: symlink releases//data → /opt/infra/xint/data/ immediately after install so runtime state survives upgrades.