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/.

subjects.njk

@@ -10,11 +10,17 @@ permalink: /subjects/
 <section class="subject-group">
   <h2>{{ subject }}</h2>
   <ul>
+    {#- collections[subject] is Eleventy's automatic per-tag collection, so it
+        picks up drafts too whenever they are in collections at all (dev). They
+        are excluded outright in a production build; this keeps the local page
+        honest as well, so /subjects/ always mirrors what is actually live. -#}
     {%- for post in collections[subject] | sort(true, false, "date") %}
+    {%- if not post.data.draft %}
     <li>
       <a href="{{ post.url }}">{{ post.data.title | inlineMarkdown | safe }}</a>
       <time datetime="{{ post.date | isoDate }}">{{ post.date | readableDate }}</time>
     </li>
+    {%- endif %}
     {%- endfor %}
   </ul>
 </section>