[doc] Install sphinx_autorun for the Jenkins doc build

conf.py enables the sphinx_autorun extension, but it is not part of the
triqs base image (triqs itself does not use it) and was not installed by
jenkins/Dockerfile, so the ubuntu-clang doc build failed with
"Could not import extension sphinx_autorun".

- Add python3-sphinx-autorun to the Jenkins image apt install
- Add sphinx_autorun to the configure-time doc dependency check so a
  missing extension fails early with a clear message instead of midway
  through sphinx-build

Assisted-by: Claude <noreply@anthropic.com>

Author: Wentzell

doc/CMakeLists.txt

@@ -1,7 +1,7 @@
 # Fail early if a doc dependency is missing (import names, not distribution names)
 find_package(Python COMPONENTS Interpreter REQUIRED)
 
-foreach(_module numpydoc nbsphinx myst_parser linkify_it sphinx_rtd_theme matplotlib)
+foreach(_module numpydoc nbsphinx myst_parser linkify_it sphinx_rtd_theme matplotlib sphinx_autorun)
   execute_process(
     COMMAND ${Python_EXECUTABLE} -c "import ${_module}"
     RESULT_VARIABLE _rc OUTPUT_QUIET ERROR_QUIET)

jenkins/Dockerfile

@@ -2,7 +2,7 @@
 FROM flatironinstitute/triqs:unstable-ubuntu-clang
 
 # Install missing system dependencies
-RUN apt-get update && apt-get install -y meson ninja-build python3-setuptools python3-skimage python3-tomli
+RUN apt-get update && apt-get install -y meson ninja-build python3-setuptools python3-skimage python3-tomli python3-sphinx-autorun
 
 ENV OMP_NUM_THREADS=1