spread the demo's features across the pages that would carry them

notes-on-water had become a kitchen sink: every feature from the last eight
loops on one page, which demonstrates the engine and misrepresents the site.

Now each lands where a real site would put it. The text marks, the abbreviation,
authored <kbd> and the margin note go to writing/typography, which is already
the page about what the engine does to words. Icons and the grouped panels go to
pages/colophon, which is the page about the theme — install instructions are
what tabs are actually for. about gets a lone expando, the-flood gets a chapter
note, and notes-on-water keeps what it is really for: the include and its
namespaced footnotes, the gauge table, the glossary and a contents list over its
own headings.

Seven bundles carry features now instead of two, and the demo cases moved with
them, so each still names the page it proves.

examples/demo-site/content/pages/colophon.en.md

@@ -6,3 +6,18 @@ Built by khosra: one Go binary, four dependencies, no JavaScript anywhere in the
 The stylesheet is inlined into every page, so a site root with no `static/` still renders. A real theme would
 replace it, and `templates/list.html` in this site root shows how — that one file overrides a single named
 block and inherits the rest of the document.
+
+:tip: An icon is a name the engine hands to the theme; this reference theme answers with a character, while a
+theme of your own might answer with an SVG. A name it does not know, like :nosuchicon:, keeps its text.
+
+:::details{group=run summary="Serve the demo" open=yes}
+`make demo` — this site, on `localhost:8080`.
+:::
+
+:::details{group=run summary="Serve your own"}
+`khosra -site /path/to/site`. Grouped panels open one at a time, and nothing here runs a script.
+:::
+
+:::tip{title="Nothing is hidden"}
+Panels are `<details>`, which every browser opens without help. A reader with scripting off sees the same page.
+:::