Retract the seven published columns into drafts/ and promote the 24 per-date
entries split out of Notes/random.md. Bodies are verbatim; titles, subjects
and slugs are new.
Make publication a matter of location. Notes/Notes.11tydata.js gives anything
under Notes/ permalink: false unless tagged `column`; drafts/drafts.11tydata.js
renders drafts at their real permalink under `yarn dev` and excludes them from
collections entirely in a build, so no template can surface one. Publishing is
now `git mv drafts/<file> columns/`, and moving it back retracts it.
Untagged notes were previously rendered into _site/ and deployed — including
Notes/random.md, which was live at /Notes/random/.
- Drive the columns collection from the `column` tag, recovering 3 columns
authored under Notes/ that the glob missed
- Tag the 6 columns with subject tags; add a subjects collection and a
/subjects/ listing page (newest-first), linked from the footer
