docs: add PrepareTools example notebook

[Copilot]

Adds a MyST Notebook example demonstrating the PrepareTools API, following the same conventions as the existing repair_tools.mystnb example.

Changes

• doc/source/examples/05_tools/prepare_tools.mystnb – New example notebook covering:
  • extract_volume_from_faces / extract_volume_from_edge_loops – fluid domain extraction from a hollow cylinder
  • remove_rounds – fillet removal for mesh simplification
  • share_topology – conformal topology merging between adjacent bodies
  • detect_helixes – screw thread detection on a bolt model
  • create_box_enclosure / create_sphere_enclosure – enclosure generation with EnclosureOptions
  • detect_sweepable_bodies – sweepability check with optional source/target face retrieval
• doc/source/examples.rst – Added prepare_tools.mystnb to the Tools examples gallery; updated section description to reference both RepairTools and PrepareTools
• doc/source/conf.py – Added nbsphinx_thumbnails entry for the new example
• doc/source/_static/thumbnails/prepare_tools.png – Thumbnail for the gallery card

All geometry files are downloaded at runtime from the repository's tests/integration/files/ directory (same pattern as repair_tools.mystnb).

Issue linked

Resolves the request to document PrepareTools with a worked example.

Checklist

• I have tested my changes locally.
• I have added necessary documentation or updated existing documentation.
• I have followed the coding style guidelines of this project.
• I have added appropriate unit tests.
• I have reviewed my changes before submitting this pull request.
• I have linked the issue or issues that are solved to the PR if any.
• I have assigned this PR to myself.
• I have added the minimum version decorator to any new backend method implemented.
• I have made sure that the title of my PR follows Conventional commits style (e.g. feat: extrude circle to cylinder)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Create an example for PrepareTools</issue_title>
<issue_description>Using the doc/source/contributing.rst file section on Adding examples, add an example for how to use the methods in the PrepareTools class.

Use the example template in doc/source/examples/99_misc to guide you. If you need specific files, use files from tests/integration/files</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Create an example for PrepareTools #2640

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