Render through a desynchronized WebGL context by default

Measured click-to-paint was 72-77 ms, of which the editor itself spends
under 4 ms; the rest is the finished frame waiting in the compositor
queue. A desynchronized context bypasses it (16-18 ms in the same probe).
Pixi has no option for it, so main.ts builds the WebGL2 context itself.
The mode may tear on some drivers; ?vsync falls back to Pixi's own
context.

__gm.lowLatency() reports the attributes the browser actually granted,
and a graph-step check pins that the mode stays on.

Also adds the todo note graph-node-collapse-width.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -549,6 +549,10 @@ selected and switched back on.
 ## Stack
 
 - **PixiJS v8** – rendering and pointer events. No game engine; runtime systems live in `src/runtime/`.
+  `main.ts` creates the WebGL context itself with `desynchronized`, which Pixi has no option for:
+  frames skip the compositor queue, so the UI keeps up with the pointer (click to picture measured
+  72–77 ms before, 16–18 ms after). The price is possible tearing while things move fast;
+  `?vsync` falls back to Pixi's own context. A browser without the mode simply ignores it.
 - **Own canvas widget toolkit** (`src/ui/`) – panels, buttons, lists, text/number/color fields,
   popups. The only lasting DOM element is a hidden `<input>` used as a keyboard bridge (IME,
   mobile keyboard, clipboard) while a canvas text field is focused; *Upload…* adds a short-lived
@@ -640,7 +644,7 @@ npm run check        # typecheck + lint + format:check + tests, what CI would ru
                      #   code is lost (tail's is reported), so a red run reads as green
 npm run build        # writes dist/ and regenerates index.html
 export GM_REMOTE=user@host                                    # optional: run the browser elsewhere; see below
-node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 534 editor checks, screenshots in /tmp/gm-e2e-*.png
+node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 535 editor checks, screenshots in /tmp/gm-e2e-*.png
 GM_STEPS=20 node tools/e2e.mjs                                # or 1-12, or 6,20 – a subset while working on one step
 ./e2e.sh start [GM_STEPS]                                     # the same run detached, see below
 ./e2e.sh status                                               # live progress, or the last run's result