Split THD bearing tutorials and document rotor rotation / coordinate axes

[ViniciusTxc3]

Summary

• Document ROSS’s assumed counterclockwise rotation and coordinate axes in the modeling tutorial, with a new figure (rotor_direction.svg).
• Split the large THD bearings tutorial into smaller notebooks so pages load faster and are easier to navigate on the documentation site.
• Register the new notebook in the user guide toctree.

Motivation

The THD bearings tutorial previously packed PlainJournal, TiltingPad, ThrustPad, and SqueezeFilmDamper into a single notebook. With many executed outputs (plots, tables), that page was very heavy for Sphinx / Jupyter Book and for readers.

Splitting the content into focused notebooks improves:

• Site loading and build performance — smaller pages and less content rendered at once
• Navigation and readability — journal bearings vs thrust / SFD in separate pages
• Maintenance — updates can be scoped to one topic without editing a monolithic notebook

Change

1. Rotor direction and coordinate axes (tutorial_part_1_1.ipynb)

• New section explaining that ROSS assumes counterclockwise rotation and the shaft along the z-axis.
• New figure: docs/_static/img/rotor_direction.svg.
• Notes that other conventions require adapting inputs and result interpretation.

2. Split THD bearing tutorials

Notebook	Content
tutorial_bearings_part_1.ipynb	General / parametric classes (unchanged scope); TOC updated for the new split
tutorial_bearings_part_2.ipynb	THD journal bearings only: PlainJournal, TiltingPad
tutorial_bearings_part_2_2.ipynb (new)	THD thrust & SFD: ThrustPad, SqueezeFilmDamper

3. Docs navigation (user_guide.md)
   Added tutorial_bearings_part_2_2 to the Tutorials toctree so the new page appears in the docs sidebar.