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/process-mods.sh

@@ -22,10 +22,20 @@ OUT_DIR="$MODDING_ROOT/dist/mods"
 [ -d "$DATA_DIR" ] \
     || { echo "Game data not found at $DATA_DIR - see the root README.md section 3." >&2; exit 1; }
 
+echo "== Staging a patched copy of hacked/ for mdlp to build against =="
+# mdlp's own go.mod points a `replace` at the sibling ../hacked - stage a
+# patched copy here (never build src/hacked/ in place) so mdlp picks up the
+# same fixes hacked's own binary does (see src/hacked-patches/).
+SCRATCH_DIR="$MODDING_ROOT/build/mdlp-src"
+rm -rf "$SCRATCH_DIR"
+mkdir -p "$SCRATCH_DIR"
+bash "$MODDING_ROOT/mdlp-image/stage-hacked.sh" "$MODDING_ROOT" "$SCRATCH_DIR/hacked"
+cp -a "$MODDING_ROOT/src/mdlp" "$SCRATCH_DIR/mdlp"
+
 echo "== Building mdlp =="
 BIN_DIR="$(mktemp -d)"
 trap 'rm -rf "$BIN_DIR"' EXIT
-(cd "$MODDING_ROOT/src/mdlp" && go build -trimpath -o "$BIN_DIR/mdlp" .)
+(cd "$SCRATCH_DIR/mdlp" && go build -trimpath -o "$BIN_DIR/mdlp" .)
 
 MDLP_ARGS=(-data "$DATA_DIR" -mods "$MODDING_ROOT/mods" -out "$OUT_DIR")
 if [ -n "${MODS:-}" ]; then