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/.

drafts/drafts.11tydata.js

@@ -0,0 +1,35 @@
+// Drafts are visible on the dev server and nowhere else.
+//
+// ELEVENTY_RUN_MODE is "serve" or "watch" under `yarn dev`, and "build" under
+// `yarn build` — which is the only thing CI and the Dockerfile ever run. So the
+// gate fails safe: a draft can be previewed at its real permalink locally, but
+// no code path that produces a deployable _site/ will emit one.
+//
+// Collection membership is itself gated on the run mode, and that is the hard
+// guarantee rather than a courtesy:
+//
+//   build  — a draft belongs to NO collection, so no template can render its
+//            title, date, or URL even by accident. Eleventy auto-creates a
+//            collection per tag, and drafts carry `tags: [column, <subject>]`
+//            so that promoting one is a plain `git mv`. That means they land
+//            in collections.philosophy and friends, which /subjects/ iterates
+//            directly — it listed every draft with href="false" until this
+//            gate existed. Filtering the two hand-written collections was not
+//            enough; only excluding them wholesale is.
+//   serve  — a draft joins collections so /drafts/ can enumerate them. The
+//            `draft` flag then keeps them out of the homepage and the sidebar
+//            (see .eleventy.js) and out of /subjects/ (see subjects.njk), so
+//            every page except /drafts/ shows exactly what production shows.
+//
+// Promoting a draft is `git mv drafts/x.md columns/`: the front matter is
+// already complete and correct, and leaving this directory is what publishes it.
+
+const PREVIEW = process.env.ELEVENTY_RUN_MODE !== "build";
+
+module.exports = {
+  draft: true,
+  eleventyExcludeFromCollections: !PREVIEW,
+  eleventyComputed: {
+    permalink: (data) => (PREVIEW ? data.permalink : false),
+  },
+};