chore(vk): keep the two chosen covers, drop the rest

The dark and light covers move up beside the generator as the shipped assets;
the six exploratory variants and the contact sheet go.

Trims the generator to match: VARIANTS is now only the two covers, and with the
retired variants gone so are the knobs nothing reaches any more — the wordmark
caption, the branded palette, the whole-board height fit and the non-brand tile
face. Left behind, they would read as supported options that no output exercises.

`node build-cover.mjs` now reproduces exactly the two committed PNGs.

assets/vk/cover/README.md

@@ -3,14 +3,20 @@
 The cover art for the VK community (`1920×768`). The community avatar — the «Э» tile — is
 uploaded separately; this is only the backdrop behind it.
 
-`build-cover.mjs` is the whole thing: a small software renderer that draws an Эрудит board in
-perspective with the opening `ГРАМОТНОСТЬ / СОПЕРНИК / ЭРУДИЦИЯ / УМ` already played, and
-emits one PNG per art-direction variant plus a contact sheet.
+| File | What |
+|------|------|
+| `cover-night-spot.png` | the dark cover — board in a warm spotlight |
+| `cover-day-spot.png` | the light cover — same camera, same crop, daylight |
+| `build-cover.mjs` | the generator both are rendered by |
+
+`build-cover.mjs` is a small software renderer that draws an Эрудит board in perspective with
+the opening `ГРАМОТНОСТЬ / СОПЕРНИК / ЭРУДИЦИЯ / УМ` already played, and writes the two PNGs
+next to itself.
 
 ```sh
 cd assets/vk/cover
-node build-cover.mjs                # every variant -> preview/
-node build-cover.mjs night-spot     # one variant
+node build-cover.mjs                # both covers
+node build-cover.mjs night-spot     # one of them
 FAST=1  node build-cover.mjs        # 1x instead of 2x supersampling, for quick iteration
 ZONES=1 node build-cover.mjs        # overlay the VK keep-outs on the render
 LAYOUT=cross node build-cover.mjs   # the alternative word arrangement