- Rename ChannelVisibility.PUBLIC to ChannelVisibility.COMMUNITY
- Update stored value from 'public' to 'community' across model, schema, API, CLI, and frontend
- Add Alembic migration to update existing database rows
- Consolidate upgrade docs: merge v0.11.0, v0.12.0, v0.13.0 into single v0.11.0 section
- Add i18n visibility level translation keys (en, nl)
- Update section headings on channels page to use t() for i18n
- Keep visibility badges lowercase per UI design