Create documentation and tutorials

## Summary
Create comprehensive documentation and tutorials for the HTFA toolbox.

## Tasks
### Documentation
- [ ] Set up Sphinx documentation framework
- [ ] Write API documentation for all classes and methods
- [ ] Create installation and quick start guides
- [ ] Add theoretical background and algorithm explanations
- [ ] Write troubleshooting and FAQ sections
- [ ] Set up automated documentation deployment

### Tutorials
- [ ] Create basic TFA usage tutorial (single subject)
- [ ] Create HTFA tutorial for multi-subject analysis
- [ ] Add visualization examples using matplotlib
- [ ] Create performance optimization guide
- [ ] Add real-world neuroimaging data examples
- [ ] Create Jupyter notebook tutorials

### Sample Data
- [ ] Curate small sample neuroimaging datasets
- [ ] Create synthetic data generation examples
- [ ] Add data loading and preprocessing utilities
- [ ] Document data format requirements

## Documentation Framework
- Use Sphinx with RTD theme
- Host on Read the Docs
- Include notebook tutorials via nbsphinx
- Automated API docs from docstrings

## Acceptance Criteria
- Complete API documentation
- At least 3 comprehensive tutorials
- Documentation builds without errors
- Tutorials run successfully with sample data