Build wgrib2 with NCEPLIBS-g2c for PNG + AEC decoder support

The previous attempt to flip `-DUSE_PNG=ON -DUSE_AEC=ON` on wgrib2
broke the image build because wgrib2 v3.6.0's CMakeLists.txt
line 94 forces `find_package(g2c 1.9.0 REQUIRED)` whenever PNG or
JPEG2000 is enabled, and NCEPLIBS-g2c wasn't installed in the
wgrib2-builder stage.

Install NCEPLIBS-g2c v1.9.0 (the version wgrib2 asks for) in the
wgrib2-builder stage ahead of wgrib2 itself, with:

  - USE_PNG=ON           (needs libpng-dev, already present)
  - USE_AEC=ON           (needs libaec-dev, already present)
  - USE_Jasper=OFF       (default ON — would need libjasper-dev
                          and another runtime dep we don't need)
  - USE_OpenJPEG=OFF     (same rationale)
  - BUILD_G2C=OFF        (new experimental API, not needed here)

Then flip wgrib2's PNG/AEC flags back on. wgrib2's binary links
dynamically against libg2c.so so the final stage copies
/usr/local/lib/libg2c.so* from the builder and refreshes the
loader cache with ldconfig.

With the decoder restored, re-add MrmsFetchWorker to the prod
cron in runtime.exs. That worker pulls NOAA MRMS PrecipRate grids
every 2 minutes, which use GRIB2 DRT 5.41 (PNG-compressed) — the
whole reason we needed the PNG decoder in the first place. ASOS
nudges will now have a live radar overlay again.

Dockerfile

@@ -22,26 +22,45 @@ ARG RUNNER_IMAGE="docker.io/debian:${DEBIAN_VERSION}"
 FROM ${RUNNER_IMAGE} AS wgrib2-builder
 
 ARG WGRIB2_VERSION=3.6.0
+ARG G2C_VERSION=1.9.0
 
 RUN apt-get update \
   && apt-get install -y --no-install-recommends \
-     build-essential gfortran cmake wget ca-certificates \
+     build-essential gfortran cmake wget ca-certificates pkg-config \
      zlib1g-dev libaec-dev libpng-dev \
   && rm -rf /var/lib/apt/lists/*
 
+# NCEPLIBS-g2c: wgrib2 >= 3.x requires this via find_package whenever
+# PNG / JPEG2000 decoders are enabled (wgrib2 CMakeLists:94). We only
+# need PNG (MRMS PrecipRate / native HRRR) + AEC — Jasper/OpenJPEG
+# default to ON in g2c and must be explicitly disabled since libjasper
+# isn't installed in this stage and would pull another runtime dep
+# into the debian-slim runner.
+WORKDIR /tmp/g2c
+RUN wget -q --content-disposition "https://github.com/NOAA-EMC/NCEPLIBS-g2c/archive/refs/tags/v${G2C_VERSION}.tar.gz" \
+      -O g2c.tar.gz \
+  && tar xzf g2c.tar.gz \
+  && cd NCEPLIBS-g2c-${G2C_VERSION} \
+  && mkdir build && cd build \
+  && cmake .. -DCMAKE_INSTALL_PREFIX=/usr/local \
+              -DCMAKE_BUILD_TYPE=Release \
+              -DUSE_PNG=ON \
+              -DUSE_AEC=ON \
+              -DUSE_Jasper=OFF \
+              -DUSE_OpenJPEG=OFF \
+              -DBUILD_G2C=OFF \
+  && make -j$(nproc) \
+  && make install
+
 WORKDIR /tmp/wgrib2
 
-## NOTE: wgrib2 3.6.0 enabling -DUSE_PNG / -DUSE_AEC triggers a hard
-## find_package(g2c 1.9.0 REQUIRED) for NCEPLIBS-g2c, which isn't
-## installed here. Until that's addressed, the stock build stays —
-## MRMS PrecipRate (packing type 41) can't be decoded, so
-## MrmsFetchWorker is kept out of the prod cron.
 RUN wget -q --content-disposition "https://github.com/NOAA-EMC/wgrib2/archive/refs/tags/v${WGRIB2_VERSION}.tar.gz" \
       -O wgrib2.tar.gz \
   && tar xzf wgrib2.tar.gz \
   && cd wgrib2-${WGRIB2_VERSION} \
   && mkdir build && cd build \
   && cmake .. -DCMAKE_INSTALL_PREFIX=/usr/local -DCMAKE_BUILD_TYPE=Release \
+       -DUSE_PNG=ON -DUSE_AEC=ON \
   && make -j$(nproc) \
   && make install \
   && strip /usr/local/bin/wgrib2
@@ -120,6 +139,12 @@ WORKDIR "/app"
 RUN chown nobody /app
 
 COPY --from=wgrib2-builder /usr/local/bin/wgrib2 /usr/local/bin/wgrib2
+# wgrib2 links dynamically against libg2c.so from the builder stage —
+# carry it across and refresh the loader cache so /usr/local/lib is
+# searched at exec time.
+COPY --from=wgrib2-builder /usr/local/lib/libg2c.so* /usr/local/lib/
+RUN ldconfig
+
 COPY --from=builder --chown=nobody:root /app/_build/${MIX_ENV}/rel/microwaveprop ./
 
 USER nobody

config/runtime.exs

@@ -215,13 +215,12 @@ if config_env() == :prod do
          # Hourly cron caused overlapping/failed runs because one full sweep
          # exceeds a 60-minute window.
          {"5 */3 * * *", Microwaveprop.Workers.PropagationGridWorker},
-         # MrmsFetchWorker is intentionally absent: the prod wgrib2 build
-         # doesn't have the PNG decoder (DRT 5.41) that MRMS PrecipRate
-         # uses, so every fetch failed with "packing type 41 not
-         # supported". AsosAdjustmentWorker gracefully handles an empty
-         # MRMS cache — the rain overlay is a nice-to-have, the ASOS
-         # nudge still runs on its own. Re-add once the Dockerfile
-         # installs NCEPLIBS-g2c + rebuilds wgrib2 with -DUSE_PNG=ON.
+         # MRMS refreshes the PrecipRate cache that AsosAdjustmentWorker
+         # overlays onto the score grid. Both must run together — an
+         # ASOS nudge without a fresh MRMS frame reverts to HRRR-only
+         # rain. Requires wgrib2 built with PNG decoder support (DRT
+         # 5.41), which the Dockerfile now enables via NCEPLIBS-g2c.
+         {"*/2 * * * *", Microwaveprop.Workers.MrmsFetchWorker},
          {"*/10 * * * *", Microwaveprop.Workers.AsosAdjustmentWorker},
          {"*/15 * * * *", Microwaveprop.Workers.PropagationPruneWorker},
          {"*/30 * * * *", Microwaveprop.Workers.BackfillEnqueueWorker,