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>

src/editor/debugHook.ts

@@ -281,6 +281,9 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
       };
     },
     fps: () => editor.fps,
+    lowLatency: () =>
+      (app.renderer as unknown as { gl?: WebGL2RenderingContext }).gl?.getContextAttributes()
+        ?.desynchronized === true,
     tab: () => editor.tab,
     showTab: (tab: CentreTab) => editor.showTab(tab),
   };