Adding modding folder with a hacked build.

modding/Makefile

@@ -0,0 +1,30 @@
+# Builds the modding subproject - see README.md.
+#
+# Targets:
+#   all (default)   - alias for `hacked`.
+#   build-image      - builds the hacked-build-image Docker image
+#                       (./hacked-build-image.sh). Only needed once, or after
+#                       hacked-build-image/ or hacked/go.mod|go.sum changes.
+#   hacked           - compiles hacked/ for Linux and Windows via that image,
+#                       offline. Output lands in dist/.
+#   clean            - removes dist/.
+.PHONY: all build-image hacked clean
+
+all: hacked
+
+build-image:
+	./hacked-build-image.sh
+
+# If we're already running inside the hacked-build-image
+# (HACKED_BUILD_IMAGE, set by its Dockerfile), compile directly instead of
+# trying to docker-run it again - e.g. a CI job already using this image as
+# its container. Otherwise, run it via Docker as usual.
+hacked:
+	@if [ -n "$$HACKED_BUILD_IMAGE" ]; then \
+		bash hacked-build-image/build-hacked.sh; \
+	else \
+		./hacked-build-run-image.sh; \
+	fi
+
+clean:
+	rm -rf dist