Stop blocking native scroll on the YES canvas's touch handlers

The real cause of the scroll jump, confirmed by "doesn't jump before
yes loads": preventDefault() on touchstart/touchmove was inherited
from the original standalone page (where it was harmless - nothing
else on the page to scroll to). Embedded as a hero, .hero-canvas
covers the entire first screen, so any touch-scroll gesture starting
there fought against blocked native scroll the whole time this
component was mounted. The position tracking these handlers do (for
the cosmetic line-cluster wiggle) never needed default prevented -
just switched to passive listeners so the browser scrolls natively.

yes.js

@@ -106,27 +106,31 @@ export class RasterizedYES {
             updatePosition(e.clientX, e.clientY);
         });
 
-        // Scoped to the canvas itself, not `window` - the original
+        // Scoped to the canvas itself, not `window` (see below), and
-        // standalone page was the whole document, so preventDefault()ing
+        // no longer calling preventDefault(): the original standalone
-        // touchmove globally was harmless (nothing else to scroll to).
+        // page was the whole document, so blocking default touch
-        // Embedded as a hero above a longer page, that same global
+        // behavior was harmless (nothing else to scroll to). Embedded
-        // handler silently blocks scrolling everywhere, not just over
+        // as a hero above a longer page, .hero-yes covers the entire
-        // the canvas - this only intercepts touches that start there.
+        // first screen - preventDefault() here was fighting the
+        // browser's own native scroll for any touch gesture starting
+        // in that region, which is what actually caused scrolling to
+        // jump/stutter (only once this component had mounted and
+        // attached these listeners - a plain page scroll never needed
+        // default prevented in the first place, just the position for
+        // the cosmetic line-cluster tracking below).
         this.lineCanvas.addEventListener('touchmove', (e) => {
-            e.preventDefault();
             if (e.touches.length > 0) {
                 const touch = e.touches[0];
                 updatePosition(touch.clientX, touch.clientY);
             }
-        }, { passive: false });
+        }, { passive: true });
 
         this.lineCanvas.addEventListener('touchstart', (e) => {
-            e.preventDefault();
             if (e.touches.length > 0) {
                 const touch = e.touches[0];
                 updatePosition(touch.clientX, touch.clientY);
             }
-        }, { passive: false });
+        }, { passive: true });
 
         this.mouseX = 0.5;
         this.mouseY = 0.5;