docs(pytest): add pytest test item manual section

New test_items/pytest_test_item.rst (params, host-subprocess execution,
pytest-must-be-installed note), wired into the toctree. Regenerated PDF.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

doc/manual/sphinx/source/test_items/pytest_test_item.rst

@@ -0,0 +1,50 @@
+**pytest** test item
+============================================================
+
+The ``pytest`` test item runs a `pytest <https://docs.pytest.org>`_ test
+file and turns every collected test into a child item, each with its own
+``PASS`` / ``FAIL`` / ``SKIP`` result, duration and failure message. It is the
+pytest counterpart of the ``unittest`` test item.
+
+The tum file prototype is as followed:
+
+.. code-block:: yaml
+    :caption: ``pytest`` test item usage example
+
+    - pytest:
+        name: pytest test item
+        test_file: test_device.py
+        test_method:
+            - test_boot
+            - test_version
+
+Attributes
+------------------
+
+Beside common test items attributes, the pytest test item has specific
+attributes:
+
+* ``test_file``: the name (and eventually path) of the pytest file to run.
+* ``test_method``: optional list of test function names. When present, only
+  the matching tests are included in the test tree (the name is matched
+  against the function part of each pytest *node id*, the parametrisation
+  suffix being ignored). Otherwise every collected test in the file is run.
+
+Host execution
+------------------
+
+Unlike ``unittest`` (which runs in *testium*'s own interpreter), the
+``pytest`` item runs pytest in a **subprocess on the host interpreter** — the
+same one used by ``py_func`` / ``lua_func`` (overridable with the
+``python_bin`` global variable). As a consequence:
+
+* ``pytest`` (and the test's own dependencies) must be installed on that host
+  interpreter — e.g. ``pip install pytest``. It is not bundled with *testium*.
+* the tests run isolated from *testium*'s in-process API; they are meant to be
+  self-contained (they exercise the device/software under test, not the
+  *testium* tree).
+
+The item is invoked with a controlled pytest configuration
+(``--capture=no``, user ``addopts`` neutralised, cache disabled); a small
+built-in pytest plugin reports the collected tests and their results back to
+*testium*.

doc/manual/sphinx/source/tum_syntax.rst

@@ -270,6 +270,7 @@ step list attributes.
    test_items/run_test_item.rst
    test_items/sleep_test_item.rst
    test_items/unittest_test_item.rst
+   test_items/pytest_test_item.rst