* ci: add nightly build workflow for images + helm chart
Nightly build of backend/frontend/provisioner images and the helm chart,
pushed to GHCR with nightly + nightly-YYYYMMDD tags (latest stays on v*
releases). amd64 only. Gated to the upstream repo (bytedance/deer-flow).
Documented in RELEASING.md.
* ci(nightly): harden chart patch + dedupe config_version check
Address PR #4050 review feedback:
- Gate the in-workflow chart patches with grep assertions so a drifted
Chart.yaml/values.yaml fails loudly instead of silently shipping a chart
that pulls the release `latest` images (sed exits 0 on zero matches).
- Suffix the nightly chart version with the short SHA
(<base>-nightly.<date>-<sha>) so a same-day re-dispatch re-publishes
cleanly; OCI chart versions are immutable and otherwise collide.
- Note in the image-tags comment that :nightly-<date> is mutable within a
day and :sha-<short> is the only truly immutable pin.
- Extract the config_version drift check into scripts/check_config_version.sh,
shared by chart.yaml and nightly.yaml, so the parsing logic lives in one
place.
