Extract shared cmake modules into ros2_medkit_cmake ament package

[bburda]

Summary

The Jenkins ROS buildfarm fails on ros2_medkit_serialization (and potentially other packages) because shared cmake modules (ROS2MedkitCompat, ROS2MedkitCcache, ROS2MedkitLinting) in the top-level cmake/ directory are referenced via relative paths (../../cmake). On the buildfarm, each package is built as an isolated Debian package from a tarball - the parent workspace structure doesn't exist, so the includes fail.

Errors:

CMake Error at CMakeLists.txt:10 (include):
  include could not find requested file: ROS2MedkitCompat

CMake Error at CMakeLists.txt:34 (medkit_find_yaml_cpp):
  Unknown CMake command "medkit_find_yaml_cpp".

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Proposed solution

Create a new src/ros2_medkit_cmake/ ament package (standard ROS 2 pattern, like ament_cmake_core) that:

1. Ships the three cmake modules via install(FILES ... DESTINATION share/ros2_medkit_cmake/cmake)
2. Uses an ament *-extras.cmake hook to auto-add the install path to CMAKE_MODULE_PATH
3. Installs .clang-tidy alongside the modules so ROS2MedkitLinting.cmake can find it

All 11 consuming packages migrate from list(APPEND CMAKE_MODULE_PATH ...) to find_package(ros2_medkit_cmake REQUIRED) with <buildtool_depend> in package.xml.

Checklist:

• Create ros2_medkit_cmake package (CMakeLists.txt, package.xml, extras.cmake)
• Move cmake modules from cmake/ to src/ros2_medkit_cmake/cmake/
• Fix .clang-tidy path in ROS2MedkitLinting.cmake
• Migrate all 11 consuming packages (CMakeLists.txt + package.xml)
• Clean build + unit tests pass
• Update selfpatch_demos Dockerfiles (separate repo)
• Update CLAUDE.md references

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Additional context

Jenkins buildfarm log: jenkins_buildfarm.txt (build of ros-jazzy-ros2-medkit-serialization-0.3.0)