fix(reader): smooth pinch-zoom and pan for scrolled-mode PDF (#4817)

Bumps foliate-js to readest/foliate-js#43. In scrolled-mode PDF the page now zooms live under a pinch and commits without a layout shift (the inter-page gap scales with the zoom so the committed layout matches the transform-scaled preview, and the centre page is restored to its pre-commit on-screen rect), a page zoomed wider than the viewport is pannable horizontally, and the page iframes stay interactive when idle so native text selection keeps working. readest already drives the renderer's pinchZoom on a two-finger gesture, so the only reader-side change is the submodule bump plus a unit test for the new scroll pinch transform.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/readest-app/src/__tests__/document/fixed-layout-pinch-zoom.test.ts

@@ -0,0 +1,38 @@
+import { describe, expect, it } from 'vitest';
+
+import { computeScrollPinchTransform } from 'foliate-js/fixed-layout.js';
+
+describe('computeScrollPinchTransform', () => {
+  it('scales by the pinch ratio anchored at the viewport centre in both axes', () => {
+    // Anchoring the live preview at the viewport centre (in container
+    // coordinates) matches the post-pinch re-render, which restores the same
+    // centre point via the center anchor, so the zoom does not jump on release.
+    expect(
+      computeScrollPinchTransform({
+        ratio: 1.5,
+        scrollLeft: 0,
+        scrollTop: 2000,
+        viewportWidth: 360,
+        viewportHeight: 640,
+      }),
+    ).toEqual({
+      transform: 'scale(1.5)',
+      transformOrigin: '180px 2320px',
+    });
+  });
+
+  it('offsets the origin by the current scroll position', () => {
+    expect(
+      computeScrollPinchTransform({
+        ratio: 0.8,
+        scrollLeft: 90,
+        scrollTop: 0,
+        viewportWidth: 360,
+        viewportHeight: 640,
+      }),
+    ).toEqual({
+      transform: 'scale(0.8)',
+      transformOrigin: '270px 320px',
+    });
+  });
+});