Plan the artist platform: price calculator and fan-funded pressing

New docs/artist-platform.md: upload master and artwork with automatic
audio, artwork and rights checks; an itemised price calculator for every
customer (per-title vs per-copy lines, price-per-copy curve, lead time
from the production-timeline quote table, versioned price list); and
fan-funded campaigns that press and dropship per fan once the goal is
reached, refund otherwise. Covers goal maths, payments (charge into a
ring-fenced account, CNX as seller of record, legal opinion first; the
Qrates failure as the design rule), repress pre-orders, architecture on
the cnx-factory stack with the public side on a fleet machine, PDPA,
phasing (calculator public early as a run-size probe, campaigns only
after first releases ship), cost and open decisions.

Backlinks from README, process flow, production timeline, revenue model,
digital factory and roadmap items 1 and 20; total investment added-scope
table gains the platform line.

docs/production-timeline.md

@@ -216,6 +216,11 @@ stages quoted separately as "typically X weeks, subject to your
 approvals". Every plant that quotes from order date and gets caught by
 a slow artist ends up explaining itself.
 
+The price calculator on the [artist platform](artist-platform.md) quotes
+from this table in exactly this form, and a fan-funded campaign shows its
+fans an estimated ship month built the same way: campaign close, plus the
+typical pre-approval stages, plus the quote above.
+
 ## Honest caveats
 
 - **No order has ever run through this plant.** These are planning