WebGPU renderer complete: dirty uploads, default limits, legacy removed, WebGPU required, warm-up (t88 phase 2d)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -2,6 +2,10 @@
 
 A falling-sand factory game in the browser, in the style of Sandustry.
 
+WebGPU is required (Chrome or Edge with a supported graphics adapter). Both looks use WebGPU;
+there is no fallback renderer. Browsers without an adapter, including Firefox on Linux in our
+checks, show a notice on the start screen. Serve the page over HTTP as described below.
+
 Every grain of sand, ore, water and fire is simulated. You fly a small bot over a side-view
 world, dig with a resonance drill and vacuum up what breaks loose. You build furnaces from
 blocks, melt ore with coal and air, and cast the metal in molds. Then you sell bars, alloys and
@@ -51,7 +55,8 @@ The controls are in the in-game notebook (N) under Controls. The basics:
 
 ## Develop
 
-You need Node (tested with 22), Python 3, and Playwright for the browser tests and screenshots:
+You need Node (tested with 22), Python 3, and Playwright for the browser tests and screenshots.
+The golden-image tests also use ImageMagick (`magick`):
 
 ```sh
 uv venv .venv