Features for first release

This issue is to discuss the minimal features before our first "public" release (i.e., release where would be comfortable sharing with a broad audience).

- [x] Able to load custom embeddings (https://github.com/cellcanvas/cellcanvas/issues/3)
- [ ] Simple docs with example workflows
- [ ] sample data plugin so people can just get up and running to test on a small section of an image
- [ ] segmentation works well for both membranes and particles
- [ ] ability to store and load trained segmentation models (#37 )
- [x] ability to export segmentation as meshes and point annotations (star file? https://github.com/cellcanvas/cellcanvas/issues/27)
- [x] pip install (https://github.com/cellcanvas/cellcanvas/issues/13)
- [ ] separate model and view (#44 )

The broader goals and scope of CellCanvas can be discussed here: https://github.com/cellcanvas/cellcanvas/issues/24

Start with the broader scope in issue #24 and review the linked items (#3, #37, #27, #13, and #44) alongside each unchecked checklist entry. No file or test entry point is named; completion requires agreed, independently verifiable work for the listed documentation, sample data, segmentation, model storage, and model/view goals.

Written by the indexing model from the issue text.