Add AI-upscaled critter/object art as a new MDL mod type

Extends the MDL system beyond text overrides: bitmaps/<label>.json
names a model/scale and resource list, and mdlp extracts each
resource's frames, runs them through an ONNX Runtime CPU upscaler
baked into mdlp-image, re-quantizes to the game's palette, and writes
the result back - same build-time pipeline as message overrides.

Adds animgallery, a standalone viewer that renders any data
directory's animated resources as an HTML/GIF gallery with a
checkbox-driven MDL JSON generator, and -only-changed to preview just
what a mod overrides against the base game.

Fixes a real data race in hacked's ChangeNotifier.hashAll() (found via
go build -race causing non-deterministic resource counts), via a new
numbered patch rather than editing the vendored source.

Adds engine-patches/, a general-fixes counterpart to
android/engine-patches/ now staged and applied to the desktop builds
too (previously unpatched): a real GL_UNPACK_ROW_LENGTH stride bug, an
audio error-logging improvement, and two critter-rendering fixes -
mod art was losing to the base game's own re-opened resource files,
and critters rendered at the wrong size/position once that was fixed,
both from how the billboard renderer derives on-screen size and
placement straight from bitmap pixel dimensions.

Updates README.md and AGENTS.md to document engine-patches/.

modding/mdlp-image/Dockerfile

@@ -11,10 +11,33 @@ FROM ubuntu:22.04
 # needs to fetch a newer toolchain over the network at build time.
 ARG GO_VERSION=1.27.1
 
+# patch: applies src/hacked-patches/ to the scratch copy of hacked/ that
+# process-mods.sh (and ../gen_animgallery.sh) stage before building against
+# it - see stage-hacked.sh. python3/pip: runs the AI upscaler below via
+# plain CPU inference (ONNX Runtime). Not a Vulkan-based tool: this image
+# has no real GPU, and Vulkan software emulation (Mesa lavapipe) gives
+# wrong colors for ML inference workloads.
 RUN apt-get update \
     && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
-        ca-certificates curl gosu \
+        ca-certificates curl gosu patch python3 python3-pip \
     && rm -rf /var/lib/apt/lists/*
+RUN pip3 install --no-cache-dir onnxruntime pillow numpy
+
+# The AI upscaler model for mdlp's upscale mod type (see ../README.md
+# section 4): RealESRGAN_x4plus_anime_6B, a 6-block RRDBNet ONNX-exported
+# from xinntao/Real-ESRGAN's anime-illustration checkpoint (BSD-3-Clause).
+# It's trained on flat-color line art, so it keeps hard sprite edges rather
+# than smoothing them the way a photo- or video-denoising model would. A
+# mod's own "model" field (upscaleDef in ../src/mdlp/upscale.go) is not
+# consulted; every resource goes through this one model. upscale_batch.py
+# resizes its fixed native 4x output down to whatever scale a mod actually
+# asks for.
+ARG UPSCALE_MODEL_URL=https://huggingface.co/skillsafe-ai/realesrgan-x4plus-anime-6b/resolve/main/model.onnx
+RUN mkdir -p /opt/upscale-model \
+    && curl -sSL -o /opt/upscale-model/model.onnx "$UPSCALE_MODEL_URL"
+COPY mdlp-image/upscale_batch.py /usr/local/bin/upscale_batch.py
+RUN chmod 755 /usr/local/bin/upscale_batch.py
+ENV UPSCALE_MODEL_PATH=/opt/upscale-model/model.onnx
 
 RUN curl -sSLO "https://go.dev/dl/go${GO_VERSION}.linux-amd64.tar.gz" \
     && tar -C /usr/local -xzf "go${GO_VERSION}.linux-amd64.tar.gz" \