v0.5.0: Windows/ARM64 and Linux/ARM64 cross targets, .deb/.msi packaging

- Cross toolchains: llvm-mingw-aarch64 (Windows ARM64; SDL3 staged from MSYS2's
  clangarm64 repo since SDL ships no MinGW ARM64 dev package) and
  clang-aarch64-linux-gnu (Linux ARM64; arm64 libc++/SDL3 via dpkg multiarch).
- Distro images: Dockerfile.linux-arm64, Dockerfile.win-arm64, Dockerfile.debian
  and Dockerfile.debian-arm64 (Debian 13 with upstream CMake, whose 3.31 gate
  cannot enable import std).
- Packaging via CPack: .deb for Ubuntu 26.04 and Debian 13 on amd64 and arm64
  (dependencies derived by dpkg-shlibdeps), portable .zip/.tar.gz, and a
  Windows .msi built with wixl (msitools) straight from the Linux cross image.
  wixl 0.106 lacks arm64, so Windows/ARM64 ships the portable zip only.
- CMake: parameterize the SDL3 MinGW triple, add install() + CPack config.
- CI: build/package jobs for both arm64 targets and both Debian packages;
  existing Linux/Windows jobs now also emit the .deb / .zip + .msi.
- scripts/: build-linux-arm64, build-windows-arm64, build-debian,
  build-debian-arm64.

scripts/build-debian-arm64.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+# Build the Debian (latest stable) Linux/ARM64 target (.deb + binary).
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+IMAGE="${OPENRA3_DEBIAN_ARM64_IMAGE:-openra3-debian-arm64:local}"
+BUILD_DIR="${1:-build/debian-arm64}"
+
+docker build --target dev -f "$ROOT/Dockerfile.debian-arm64" -t "$IMAGE" "$ROOT"
+docker run --rm -v "$ROOT:/work" -w /work "$IMAGE" cmake -S . -B "$BUILD_DIR" -G Ninja \
+    -DCMAKE_TOOLCHAIN_FILE=cmake/toolchains/clang-aarch64-linux-gnu.cmake \
+    -DCMAKE_BUILD_TYPE=Release \
+    -DOPENRA3_AARCH64_CC=clang-19 -DOPENRA3_AARCH64_CXX=clang++-19 \
+    -DOPENRA3_AARCH64_STDLIB_MODULES_JSON=/usr/lib/llvm-19/lib/libc++.modules.json \
+    -DOPENRA3_DISTRO_TAG=debian13
+docker run --rm -v "$ROOT:/work" -w /work "$IMAGE" cmake --build "$BUILD_DIR" -j
+docker run --rm -v "$ROOT:/work" -w /work "$IMAGE" bash -c "cd $BUILD_DIR && cpack -G DEB"
+
+echo "Debian arm64: $ROOT/$BUILD_DIR/bin/openra3 (+ .deb)"

scripts/build-debian.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+# Build the Debian (latest stable) target (.deb + binary) with the isolated image.
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+IMAGE="${OPENRA3_DEBIAN_IMAGE:-openra3-debian:local}"
+BUILD_DIR="${1:-build/debian}"
+
+docker build --target dev -f "$ROOT/Dockerfile.debian" -t "$IMAGE" "$ROOT"
+docker run --rm -v "$ROOT:/work" -w /work "$IMAGE" cmake -S . -B "$BUILD_DIR" -G Ninja \
+    -DCMAKE_BUILD_TYPE=Release \
+    -DCMAKE_CXX_STDLIB_MODULES_JSON=/usr/lib/llvm-19/lib/libc++.modules.json \
+    -DOPENRA3_DISTRO_TAG=debian13
+docker run --rm -v "$ROOT:/work" -w /work "$IMAGE" cmake --build "$BUILD_DIR" -j
+docker run --rm -v "$ROOT:/work" -w /work "$IMAGE" bash -c "cd $BUILD_DIR && cpack -G DEB"
+
+echo "Debian: $ROOT/$BUILD_DIR/bin/openra3 (+ .deb)"

scripts/build-linux-arm64.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+# Build the Linux/ARM64 target (.deb + binary) with the isolated cross image.
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+IMAGE="${OPENRA3_LINUX_ARM64_IMAGE:-openra3-linux-arm64:local}"
+BUILD_DIR="${1:-build/linux-arm64}"
+
+docker build --target dev -f "$ROOT/Dockerfile.linux-arm64" -t "$IMAGE" "$ROOT"
+docker run --rm -v "$ROOT:/work" -w /work "$IMAGE" cmake -S . -B "$BUILD_DIR" -G Ninja \
+    -DCMAKE_TOOLCHAIN_FILE=cmake/toolchains/clang-aarch64-linux-gnu.cmake \
+    -DCMAKE_BUILD_TYPE=Release -DOPENRA3_DISTRO_TAG=ubuntu26.04
+docker run --rm -v "$ROOT:/work" -w /work "$IMAGE" cmake --build "$BUILD_DIR" -j
+docker run --rm -v "$ROOT:/work" -w /work "$IMAGE" bash -c "cd $BUILD_DIR && cpack -G DEB"
+
+echo "Linux arm64: $ROOT/$BUILD_DIR/bin/openra3 (+ .deb)"

scripts/build-windows-arm64.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+# Build the Windows/ARM64 target (portable .zip) with the isolated cross image.
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+IMAGE="${OPENRA3_WINDOWS_ARM64_IMAGE:-openra3-windows-arm64:local}"
+BUILD_DIR="${1:-build/windows-arm64}"
+
+docker build --target dev -f "$ROOT/Dockerfile.win-arm64" -t "$IMAGE" "$ROOT"
+docker run --rm -v "$ROOT:/work" -w /work "$IMAGE" cmake -S . -B "$BUILD_DIR" -G Ninja \
+    -DCMAKE_TOOLCHAIN_FILE=cmake/toolchains/llvm-mingw-aarch64.cmake \
+    -DCMAKE_BUILD_TYPE=Release
+docker run --rm -v "$ROOT:/work" -w /work "$IMAGE" cmake --build "$BUILD_DIR" -j
+docker run --rm -v "$ROOT:/work" -w /work "$IMAGE" bash -c "cd $BUILD_DIR && cpack -G ZIP"
+
+echo "Windows arm64: $ROOT/$BUILD_DIR/bin/openra3.exe (+ .zip)"