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>

tools/e2e/06-graph.mjs

@@ -253,6 +253,10 @@ export async function graph(t) {
   //      Graph while playing shows the live highlight: hold ArrowRight → the exec edge is hot.
   const fpsEdit = await evaluate('__gm.fps()');
   check('fps readout is measured in edit mode', typeof fpsEdit === 'number' && fpsEdit > 0, `fps=${fpsEdit}`);
+  check(
+    'the canvas bypasses the compositor queue by default',
+    (await evaluate('__gm.lowLatency()')) === true,
+  );
   // Single evaluate: the readout refreshes twice a second, so read value and label together.
   check(
     'fps label is visible in the toolbar',