Features:
- ECHO exporter with manifest.json for longecho integration
- --include-db, --owner-name, --include-site CLI options for ECHO export
- HTML site generation in ECHO exports (site/ subdirectory)

Infrastructure:
- CITATION.cff for GitHub "Cite this repository" integration
- Zenodo DOI preparation (.zenodo.json)
- MIT LICENSE file
- CONTRIBUTORS.md with contribution guidelines
- ORCID: 0000-0001-6443-9897

Bug fixes:
- Fixed metadata attribute names in ECHO exporter (created -> created_at)
- Fixed longecho URL in README (queelius/longecho)
- Removed invalid provider attribute from ECHO metadata export