Artist ordering demo: configure, check, offer, fan-funded campaign

New static page docs/artist-order.html (test site /demos/artist-order/)
walking the artist platform flow end to end:

- record configurator (format, speed, discs, weight, colour, packaging,
  extras, mastering, test pressings) with a live mock-up
- track list or dropped masters read in the browser (WAV/FLAC/AIFF
  headers, sample peak and clipping), side length against the format,
  jacket and label preflight (size, dpi, CMYK), rights and gate 1
- itemised offer (per title / per copy, pass-through jacket), price per
  copy against quantity, lead time from the production timeline
- direct order or fan-funded campaign: goal = max(minimum run,
  break-even), what the artist keeps, the money rules, a simulated
  campaign (sells out / just makes it / falls short) with refund or
  go-ahead-at-minimum, and the production tracker with the three gates
  and the fan update feed

Price list demo-0.1 splits the doc's 38,000 THB per title and 132 THB per
copy into lines (estimates, each listed with its basis); defaults
reproduce the artist platform example (break-even 41, goal 100, ~548 THB
kept per copy at 100).

artist-platform.md: demo paragraph, side length per format table with
sources, VAT note on the campaign example. README bullet and layout line,
site DEMOS line and landing-page entry.

site/public/index.html

@@ -103,6 +103,17 @@ document.documentElement.setAttribute("data-theme",t);})();
         demand against installed capacity.</span>
       </a>
     </li>
+    <li>
+      <a href="demos/artist-order/">
+        <strong>Artist ordering and fan funding</strong>
+        <span>Configure a record, type the track list or drop the master
+        files and artwork (checked in the browser, nothing is uploaded), get
+        an itemised offer with the price per copy against quantity and the
+        lead time, then order directly or run a fan-funded campaign to a
+        funded or missed end and follow the production through the artist
+        approvals. Indicative demo prices.</span>
+      </a>
+    </li>
   </ul>
 
   <footer>Built from <code>site/</code> in the cnx_vinyl repository.</footer>