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/.

Notes/Notes.11tydata.js

@@ -0,0 +1,16 @@
+// Notes are private. Nothing under Notes/ is written to the site unless it is
+// tagged `column` — the same marker .eleventy.js uses to define a column,
+// which is what lets a column be authored here (do-people-think, how-to-write,
+// systems) while the raw notes beside it stay unpublished.
+//
+// permalink: false processes the file but writes no output, so an untagged
+// note has no URL at all rather than an unlinked-but-reachable one.
+
+const isColumn = (data) => (data.tags || []).includes("column");
+
+module.exports = {
+  eleventyComputed: {
+    permalink: (data) => (isColumn(data) ? data.permalink : false),
+    eleventyExcludeFromCollections: (data) => !isColumn(data),
+  },
+};