docs: port 7b2462a TOC fix for master

[magic-alt]

Description

Fixes #2216.

This PR ports the existing TOC/docs fix from commit 7b2462a to master.
It moves the motion_primitives_controllers user documentation into the standard doc/ location and updates the
central controllers index and the doc-related pre-commit ignore path accordingly.

Is this user-facing behavior change?

No.

This is a docs-only change. It does not change runtime behavior, controller APIs, or controller configuration.

Did you use Generative AI?

Yes.

OpenAI Codex (GPT-5-based assistant) was used to help draft the PR description and follow-up review response. The
final wording and changes were reviewed before posting.

Additional Information

• Scope intentionally kept minimal to match the requested fix in [Docs] motion_primitive_controller TOC is broken #2216.
• Follow-up review feedback addressed by updating the motion_primitives_controllers userdoc title to match the
  package name.

[Copilot]

Pull request overview

Ports a documentation/TOC fix for motion_primitives_controllers by moving its user documentation into the standard doc/ location and updating the central controllers index accordingly.

Changes:

• Remove the legacy motion_primitives_controllers/userdoc.rst and add motion_primitives_controllers/doc/userdoc.rst.
• Add motion_primitives_controllers/doc/README.md to be included from the new RST userdoc via MyST.
• Update doc/controllers_index.rst and .pre-commit-config.yaml to reference/ignore the new doc path.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
motion_primitives_controllers/userdoc.rst	Removed old userdoc file (legacy location).
motion_primitives_controllers/doc/userdoc.rst	New Sphinx userdoc entrypoint under doc/ and updated relative includes/paths.
motion_primitives_controllers/doc/README.md	New Markdown content intended for inclusion in the rendered user docs.
doc/controllers_index.rst	Points the controllers TOC entry to the new doc/userdoc.rst path.
.pre-commit-config.yaml	Updates doc8 ignore-path to match the new userdoc location.

---

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[Copilot]

The top-level document title uses motion_primitive_controllers (singular), but the package name (and directory) is motion_primitives_controllers (plural). This will make the generated docs/toctree title inconsistent with the rest of the repository’s controller docs and with the package.xml name. Consider renaming the heading to motion_primitives_controllers to match the actual package name.

Suggested change

	motion_primitive_controllers
	==========================================
	motion_primitives_controllers
	===========================================

[Copilot]

This doc/README.md largely duplicates the package-level motion_primitives_controllers/README.md (same prose/sections with only path tweaks). Maintaining two copies of the same documentation is likely to cause drift over time. Consider consolidating to a single source of truth (e.g., include ../README.md from the RST and adjust image paths accordingly, or generate one README from the other during docs build).

Suggested change

	## Description
	This project provides an interface for sending motion primitives to an industrial robot controller
	using the `ExecuteMotionPrimitiveSequence.action` action from
	[control_msgs](https://github.com/ros-controls/control_msgs/blob/master/control_msgs/action/ExecuteMotionPrimitiveSequence.action).
	The controller receives the primitives via the action interface and forwards them through command
	interfaces to the robot-specific hardware interface. Currently, hardware interfaces for
	[Universal Robots](https://github.com/UniversalRobots/Universal_Robots_ROS2_Driver) and
	[KUKA Robots](https://github.com/b-robotized-forks/kuka_experimental/tree/motion_primitive_kuka_driver)
	are implemented.
	- Supported motion primitives:
	- `LINEAR_JOINT`
	- `LINEAR_CARTESIAN`
	- `CIRCULAR_CARTESIAN`
	If multiple motion primitives are passed to the controller via the action, the controller forwards
	them to the hardware interface as a sequence. To do this, it first sends
	`MOTION_SEQUENCE_START`, followed by each individual primitive, and finally
	`MOTION_SEQUENCE_END`. All primitives between these two markers will be executed as a single,
	continuous sequence. This allows seamless transitions (blending) between primitives.
	The action interface also allows stopping the current execution of motion primitives. When a stop
	request is received, the controller sends `STOP_MOTION` to the hardware interface, which then
	halts the robot's movement. Once the controller receives confirmation that the robot has stopped,
	it sends `RESET_STOP` to the hardware interface. After that, new commands can be sent.
	
	This can be done, for example, via a Python script as demonstrated in the
	[`example python script`](https://github.com/UniversalRobots/Universal_Robots_ROS2_Driver/blob/main/ur_robot_driver/examples/examples.py)
	in the `Universal_Robots_ROS2_Driver` package.
	## Command and State Interfaces
	To transmit the motion primitives, the following command and state interfaces are required. All
	interfaces use the naming scheme `tf_prefix_ + "motion_primitive/<interface name>"` where the
	`tf_prefix` is provided to the controller as a parameter.
	### Command Interfaces
	## Documentation
	This file intentionally avoids duplicating the package documentation.
	The package-level [`../README.md`](../README.md) is the single source of truth for the project
	description, supported motion primitives, command/state interfaces, usage examples, and images.
	Please update that file instead of maintaining a second copy here.
	For the full documentation, see:
	- [`../README.md`](../README.md)

[christophfroehlich]

please fill out the description template as requested.

[magic-alt]

please fill out the description template as requested.

Thanks for the review. I filled out the PR description template and updated the PR body accordingly. I also fixed
the document title to match the package name for consistency. Please take another look.

[christophfroehlich]

Isn't this trying to fix the same as #2221 ?

[magic-alt]

Isn't this trying to fix the same as #2221 ?
Yes — it targets the same issue as #2221. My intent with #2312 was to provide a smaller, focused port of the original 7b2462a fix, since #2221 seems to have evolved during review. Happy to close this if you'd rather continue with #2221 only.