Draw the feature graphic as the format itself

[octopranav]

A new feature graphic for the Play listing, still drawn by design/build-icons.mjs from the tokens.

Why

Play's guidance for the feature graphic asks for three things the old one missed:

• branding that extends the icon rather than repeating it (the old one was the icon's four bars);
• a ground that doesn't blend into the store's white (it was the page's near-white ground);
• a picture of what the app is for.

The graphic is also the cover of the listing's video. When the video doesn't play by itself, Play lays its play button over the centre, which was on the bars.

What it shows

How a code works. Every character names one of 25 parts of the cell before it, five by five, so a code is a place inside a place.

• Three cells are drawn cut into their 25 parts, each lighting the part the next is drawn from, down to one doorway in brass.
• The lit parts are the real ones for St. Lawrence Market's north door, #G3RJM-8X3L1, the place in the listing's screenshots: its 3, L and 1, as the reference implementation places them.
• It uses the icon's four tints: level 1 is the ground, and levels 4, 7 and 10 are the cells. The brass is the dark theme's, which is meant to be read on a ground this deep.
• No words, so nothing to translate.
• Play's play button falls on the middle cell and leaves the door showing.

Verified

• node design/build-icons.mjs --check: 20 icons match design/tokens.json. The output is deterministic, and CI compares it byte for byte.
• 1024 × 500, 24-bit RGB with no alpha, as Play requires.
• audit/markdown.py passes. PLAY.md's graphics table describes the new graphic.