Find libmosquitto and ship it in release packages (iteration 2, step 1)

cmake/Mosquitto.cmake finds it through pkg-config; with
FRAMEASSISTANT_SHIP_MOSQUITTO=ON (all package presets) it installs
lib/libmosquitto.so.1 and Debian's copyright file and excludes the
library from the Qt bundler (D35). The build containers get
libmosquitto-dev, the test container the mosquitto broker.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docker/cross-arm64.Dockerfile

@@ -13,6 +13,7 @@ RUN dpkg --add-architecture arm64 \
         qt6-base-dev qt6-base-dev-tools qt6-declarative-dev qt6-declarative-dev-tools \
         qt6-base-dev:arm64 qt6-declarative-dev:arm64 \
         libgl-dev:arm64 libegl-dev:arm64 libvulkan-dev:arm64 libxkbcommon-dev:arm64 \
+        libmosquitto-dev:arm64 \
         qml6-module-qtquick:arm64 qml6-module-qtquick-controls:arm64 \
         qml6-module-qtquick-layouts:arm64 qml6-module-qtquick-templates:arm64 \
         qml6-module-qtqml-workerscript:arm64 qml6-module-qtquick-window:arm64 \

docker/native.Dockerfile

@@ -9,7 +9,7 @@ RUN apt-get update \
  && apt-get install -y --no-install-recommends \
         ca-certificates cmake ninja-build pkgconf file patchelf g++ \
         qt6-base-dev qt6-base-dev-tools qt6-declarative-dev qt6-declarative-dev-tools \
-        libgl-dev libegl-dev libvulkan-dev libxkbcommon-dev \
+        libgl-dev libegl-dev libvulkan-dev libxkbcommon-dev libmosquitto-dev \
         qml6-module-qtquick qml6-module-qtquick-controls qml6-module-qtquick-layouts \
         qml6-module-qtquick-templates qml6-module-qtqml-workerscript qml6-module-qtquick-window \
         qml6-module-qttest qt6-qpa-plugins qt6-wayland \

docker/test.Dockerfile

@@ -1,9 +1,10 @@
 # Test environment on top of docker/native.Dockerfile: Mesa Vulkan/GL drivers (incl. the
-# lavapipe software rasterizer), Khronos validation layers and Xvfb. See scripts/container-test.sh.
+# lavapipe software rasterizer), Khronos validation layers, Xvfb, and the mosquitto broker
+# for the MQTT integration tests. See scripts/container-test.sh.
 FROM frameassistant-build-native
 
 RUN apt-get update \
  && apt-get install -y --no-install-recommends \
         mesa-vulkan-drivers vulkan-validationlayers vulkan-tools libgl1-mesa-dri \
-        xvfb xauth fonts-dejavu-core \
+        xvfb xauth fonts-dejavu-core mosquitto \
  && rm -rf /var/lib/apt/lists/*