Fix MEDIUM-severity issues: stale Jazzy links, dead pages

[mmmarinho]

Follow-up to the HIGH-severity fixes. This PR addresses the remaining MEDIUM items found in the tutorial audit.

1. Update 11 stale distro links to Jazzy

The tutorial was updated to ROS 2 Jazzy, but 11 links still pointed at Humble/Foxy. Each target was
verified to resolve on the current Jazzy docs (via the ROS documentation and Tavily), including
several Jazzy reorganisations:

File	Old (broken/old) → New (Jazzy)
parameters_and_launch.rst	Understanding-ROS2-Parameters.html → …/Understanding-ROS2-Parameters/Understanding-ROS2-Parameters.html
parameters_and_launch.rst	Launch-Main.html → Creating-Launch-Files.html (Launch-Main.html no longer exists on Jazzy)
parameters_and_launch.rst	Concepts/Basic/About-Parameters.html (×2, humble→jazzy)
publishers_and_subscribers.rst	Concepts.html#quick-overview-of-ros-2-concepts → Concepts/Basic.html (anchor removed on Jazzy)
publishers_and_subscribers.rst	About-Quality-of-Service-Settings.html → Concepts/Intermediate/About-Quality-of-Service-Settings.html
create_interface_package.rst	About-ROS-Interfaces.html#field-types → Concepts/Basic/About-Interfaces.html#field-types (anchor kept — verified present)
interfaces.rst	About-ROS-Interfaces.html → Concepts/Basic/About-Interfaces.html
python_node_explained.rst	rclpy/blob/humble/…/timer.hpp → rclpy/blob/jazzy/…/timer.hpp
python_node_explained.rst	docs.ros2.org/foxy/api/rclpy/…/init_shutdown.html → docs.ros.org/en/jazzy/p/rclpy/api/execution_and_callbacks.html (the old docs.ros2.org/<distro>/api/ layout now 404s)
transformations/tf2.rst	docs.ros2.org/foxy/api/tf2_ros/…Buffer.html → docs.ros.org/en/jazzy/p/tf2_ros/generated/classtf2__ros_1_1Buffer.html

Note: the ros2-tutorial.readthedocs.io/en/humble/… "previous version" links (in service_servers_and_clients.rst and create_interface_package.rst) are intentional and were left unchanged.

2. Make the Gazebo "other content" page reachable

docs/source/gazebo/other_content.rst (the Gazebo and ROS2 structure sensor/topic table + entities
examples) was not in any toctree, so it was unreachable. Added gazebo/other_content to the Gazebo
toctree in docs/source/index.rst.

3. Remove three dead RST files

None of these were referenced (no toctree, :doc:, :ref:, include, or literalinclude), so
Sphinx never built them:

• docker/troubleshooting.rst — its content is already inlined under Tips and troubleshooting in docker/index.rst.
• the_pycharm_dependencies_warning.rst — orphaned reusable snippet and it contained a dangling :ref: (PyCharm is not finding the dependencies, a label defined nowhere).
• the_section_is_optional.rst — orphaned reusable snippet.

All changes are documentation-only; CI (colcon build) is unaffected.

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Created by an AI agent (OpenHands) on behalf of the user.

[mmmarinho]

👍