Swap published columns for 24 entries from random.md

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/.

.eleventyignore

@@ -0,0 +1,6 @@
+# The column template is a starting point to copy, not a page. It lives in
+# drafts/ because that is where a column starts, but drafts/ files are really
+# parsed (that is how they render on the dev server) — so without this entry
+# its placeholder `date: <YYYY-MM-DD>` fails to parse and takes the build with
+# it, and if it did parse it would list itself as an extra entry on /drafts/.
+drafts/_template.md