Fan funding: the price sets the fans needed; limited edition as a switch

The artist sets only the fan price; the number of fans needed follows from
it: the plant's 100-copy minimum, or the break-even if that is higher. The
goal selector of 6a62505 is removed from both demos.

make-a-record.html:
- step 4 leads with "Your price to fans" (input, slider from 300 THB,
  presets 800 to 2,000) and a live "You need N fans to press it, X THB in
  pre-orders", plus the price below which the minimum no longer covers
  the costs (about 640 THB at the defaults)
- limited edition is now a switch, off by default; the edition size stays
  visible but disabled until it is on, and switching it on adds the
  numbered edition to the record
- "per title" renamed for end users: "One-off, for this release", "once +
  per copy", "One-off setup", with a note that one-off costs count sides,
  not songs (a double LP has four)
- the tour lowers the price to 500 THB and back to show the fans needed
  rising from 100 to 152
artist-order.html: goal field removed, "Fans needed" label and hint.
artist-platform.md: the price-sets-the-goal decision (October 2026).

docs/artist-platform.md

@@ -245,8 +245,9 @@ Nothing goes in front of fans that the plant cannot make:
 
 ### The goal
 
-The artist sets the goal in fans. The lowest it can go is the larger of
-two numbers:
+The artist sets only the fan price; the goal, the number of fans
+needed, follows from it (decided October 2026). It is the larger of two
+numbers:
 
 - **the plant's minimum campaign run**, set by setup and stamper
   economics on the semi-automatic line (**100 copies** as a planning
@@ -254,16 +255,15 @@ two numbers:
 - **the artist's break-even**: the copies at which the fan price covers
   the per-title costs, the per-copy costs and the payment fees.
 
-Above that floor the goal is the artist's choice, for example a bigger
-first run or a round number to tell fans. A higher goal is all or nothing
-as well: if it is missed, every fan is refunded, even when the floor was
-passed. Both demos let the artist set it, with the goal shown in fans and
-as the pre-order amount (fans × fan price).
+Both demos show it in fans and as the pre-order amount (fans × fan
+price); the investor demo also says from which fan price the 100-copy
+minimum is enough (about 640 THB in the illustration; below it the
+break-even sets the goal).
 
 With the illustration above and a fan price of 1,200 THB (an example,
 not a recommendation) and payment fees of about 3.5%: break-even is
-38,000 / (1,200 − 42 − 232) ≈ **41 copies**, so the lowest goal is the
-100-copy minimum. At 100 copies the artist keeps about **546 THB a copy**, at 300
+38,000 / (1,200 − 42 − 232) ≈ **41 copies**, so the goal is the 100-copy
+minimum. At 100 copies the artist keeps about **546 THB a copy**, at 300
 about **799 THB**, because the per-title cost spreads. The calculator
 shows the artist this before launch, for any price they type in. Shipping
 is charged to the fan separately at checkout, at cost.