Adds a Sunday 06:00 UTC schedule trigger to build-base.yaml plus a
CACHE_BUST=<ISO year+week> build-arg keyed off `date -u +%G-W%V`. The
apt RUN steps in Dockerfile.base reference the arg in their command
line so BuildKit's layer hash changes when the week rolls over,
forcing apt-get update + install to re-execute and pull fresh
security updates.
The wgrib2-builder stage doesn't see CACHE_BUST so the ~5-min wgrib2
compile keeps hitting layer cache across weeks; only the apt layers
rebuild. Effective cost of the weekly job: ~2 min for the cdo /
gdal-bin reinstall.
Pre-builds the runtime base (wgrib2 + g2c + cdo + gdal-bin + locale +
runtime apt deps) into git.mcintire.me/graham/prop-base. The base
workflow is path-filtered to fire only on Dockerfile.base /
build-base.yaml changes, so version bumps stay deterministic and
explicit.
Tag convention: `wgrib2-<v>-g2c-<v>-<unixts>` for traceability +
rollback, plus `:latest` for everyday consumption.
This commit only adds the new files — the app Dockerfile + build.yaml
still build wgrib2 from source. A follow-up will swap the app
Dockerfile to FROM prop-base:latest once this image lands in the
registry.
