Document project libraries and cloud sync

[franknoirot]

Addresses the documentation follow-up for KittyCAD/modeling-app#12844 and KittyCAD/modeling-app#12836 by explaining the project-library, duplicate-copy, cloud-sync, and deletion policies now present in Zoo Design Studio.

Includes

1. Adds Project Libraries and Cloud Sync docs under Zoo Design Studio Data Management.
2. Explains the file-based project model, Directory libraries, Personal Cloud, desktop/browser differences, and moving projects between libraries.
3. Documents duplicate local copies for cloud projects, including canonical copies, the Duplicate copies badge, Review duplicate copies, and the conservative cleanup policy for Directory-library copies.
4. Documents the delete policy difference between Personal Cloud projects and cloud-backed copies shown from Directory libraries.
5. Updates Data Management, Features, Project Browser, Version Control, and Projects settings docs so the new pages are discoverable.
6. Leaves MDX-safe placeholder markers for screenshots or short tutorial videos.

How to test

Preview the Project Libraries, Cloud Sync, and Project Browser docs pages and check that the new sections match the current ZDS Home behavior.

For product spot-checking, use a cloud-synced project with an extra local copy in a Directory library and confirm the docs line up with the Duplicate copies badge and Review duplicate copies flow. Then compare deleting a project from Personal Cloud with deleting a cloud-backed copy from a Directory library; the docs should match the different confirmation copy and remote-delete behavior.