xint-runtime-data-dir-symlink-required

xint writes runtime data (api-costs.json, reliability-metrics.json) to the release-internal releases/<version>/data/ directory by default, not to a persistent location. Without symlinking, all cost tracking and reliability metrics are wiped on every version upgrade. Fix: create /opt/infra/xint/data/ outside the releases tree and symlink releases/<version>/data/opt/infra/xint/data/ immediately after installation.