fix(demos): cap build parallelism to avoid gateway OOM

Gateway has a few heavily-templated TUs (~1.6 GB RSS each); compiling
them all in parallel (one per core) OOM-killed cc1plus on many-core or
RAM-limited Docker hosts. Use a sequential executor + MAKEFLAGS='-j 2'
(peak ~3.2 GB, verified building under a 6 GB cap).

Author: mfaferek93

demos/moveit_pick_place/Dockerfile

@@ -76,7 +76,7 @@ RUN bash -c "source /opt/ros/jazzy/setup.bash && \
     rosdep update && \
     rosdep install --from-paths src --ignore-src -r -y || true" && \
     bash -c "source /opt/ros/jazzy/setup.bash && \
-    colcon build --symlink-install --cmake-args -DBUILD_TESTING=OFF"
+    MAKEFLAGS='-j 2' colcon build --executor sequential --symlink-install --cmake-args -DBUILD_TESTING=OFF"
 
 # Setup environment
 RUN echo "source /opt/ros/jazzy/setup.bash" >> ~/.bashrc && \

demos/multi_ecu_aggregation/Dockerfile

@@ -57,7 +57,7 @@ RUN bash -c "source /opt/ros/jazzy/setup.bash && \
     rosdep update && \
     rosdep install --from-paths src --ignore-src -r -y \
       --skip-keys='ament_cmake_clang_format ament_cmake_clang_tidy test_msgs example_interfaces sqlite3' && \
-    colcon build --symlink-install --cmake-args -DBUILD_TESTING=OFF"
+    MAKEFLAGS='-j 2' colcon build --executor sequential --symlink-install --cmake-args -DBUILD_TESTING=OFF"
 
 # Setup environment
 RUN echo "source /opt/ros/jazzy/setup.bash" >> ~/.bashrc && \

demos/sensor_diagnostics/Dockerfile

@@ -58,7 +58,7 @@ RUN bash -c "source /opt/ros/jazzy/setup.bash && \
     rosdep update && \
     rosdep install --from-paths src --ignore-src -r -y \
       --skip-keys='ament_cmake_clang_format ament_cmake_clang_tidy test_msgs example_interfaces sqlite3' && \
-    colcon build --symlink-install --cmake-args -DBUILD_TESTING=OFF"
+    MAKEFLAGS='-j 2' colcon build --executor sequential --symlink-install --cmake-args -DBUILD_TESTING=OFF"
 
 # Setup environment
 RUN echo "source /opt/ros/jazzy/setup.bash" >> ~/.bashrc && \

demos/turtlebot3_integration/Dockerfile

@@ -78,7 +78,7 @@ WORKDIR ${COLCON_WS}
 RUN bash -c "source /opt/ros/jazzy/setup.bash && \
     rosdep update && \
     rosdep install --from-paths src --ignore-src -r -y && \
-    colcon build --symlink-install --cmake-args -DBUILD_TESTING=OFF"
+    MAKEFLAGS='-j 2' colcon build --executor sequential --symlink-install --cmake-args -DBUILD_TESTING=OFF"
 
 # Setup environment
 RUN echo "source /opt/ros/jazzy/setup.bash" >> ~/.bashrc && \