Order demos: spine choice, artwork templates, PDF and AI uploads

User request (October 2026): the order tool needs a thin / thick spine
selection, templates for the jacket and label upload, and must accept AI
and PDF files.

Both artist demos (artist-order, make-a-record):
- Spine: thin 3 mm (one record) or thick 5 mm (two records, or a thick
  insert); a double album in a single jacket takes 5 mm, thin is then
  disabled; 7", gatefold (7 or 9 mm) and own jacket disable the row with
  the reason. Quote line 'Thick 5 mm spine' (R.spine 12 / 10 THB per
  copy, estimate from QRP 0.90 vs 0.55 USD and Kudos 137.50 GBP/order).
  Mock-up draws the spine edge to scale; caption names it.
- Templates: vector PDFs written in the browser for the current choice:
  jacket spread (back, spine, front; 633/635 x 315 mm for 12" from
  Mighty Media Discs), gatefold with an inside page, labels with a page
  per side and the dinked hole; trim and bleed boxes set, 3 mm bleed,
  5 mm safe area, folds, crop marks, guidance notes.
- Uploads accept PDF, AI (PDF-compatible) and images. PDFs are read in
  the browser (object streams inflated with DecompressionStream): page
  boxes, pages, PDF/X, creator, colour spaces, font embedding; checks
  against the chosen spine (a 5 mm spread on a 3 mm order is flagged),
  bleed, CMYK, fonts; old PostScript-only AI files are refused with the
  fix. Image spreads are measured the same way. Preview via pdf.js
  (jsDelivr, loaded only when a PDF arrives); the front panel goes into
  the mock-up.

artist-platform.md: new section 'Artwork templates and files' with the
sources; preflight step links it; RI 'left out' list updated. README
demo bullet. Checked headless on Edge: fixtures (3/5 mm spreads, no
bleed, AI, legacy AI, front only, labels, 150 dpi PNG), downloaded
templates parsed with PyMuPDF, 390/1024/1280 px no overflow, dark and
light, no page errors; pw_mr_check --tour and pw_ri unchanged
(37,836 / 232).

README.md

@@ -170,10 +170,12 @@ The detail lives in dedicated documents:
   fan-funded campaign that the plant presses and ships to each fan once
   enough have pre-ordered, with refunds if not
 - [Artist ordering demo](docs/artist-order.html): the artist platform as a
-  clickable single page: configure a record, type the track list or drop
-  the master files and artwork (checked in the browser, never uploaded:
-  format, sample rate, bit depth, clipping, side length against the
-  format, print resolution), approve gate 1, get the itemised offer with
+  clickable single page: configure a record (jacket with a 3 or 5 mm
+  spine), type the track list or drop the master files and artwork
+  (checked in the browser, never uploaded: format, sample rate, bit
+  depth, clipping, side length against the format; artwork as PDF, AI or
+  image against the downloadable jacket and label templates: size and
+  spine, bleed, resolution, colour, fonts), approve gate 1, get the itemised offer with
   its price curve and lead time, then order directly or run a fan-funded
   campaign to a funded or missed end (refund, or go ahead at the
   minimum) and follow the production through the three artist gates