fix(reader): stabilize PDF side panel resize

[yicheng47]

Summary

• Relayout PDF readers when the AI/sidebar changes width, without changing explicit numeric zoom.
• Make PDF side panel dragging use pointer capture so resize cannot stick after mouse release.
• Match the reader panel resize affordance and PDF scrollbar styling to the existing reader/sidebar behavior.
• Preserve the current PDF page row during resize relayouts.

Submodule

• Updates public/foliate-js to yicheng47/foliate-js@f647a4a.

Test plan

• pnpm exec tsc --noEmit
• pnpm run lint
• node --check public/foliate-js/pdf-scroll.js
• node --check public/foliate-js/fixed-layout.js
• git diff --check
• git -C public/foliate-js diff --check

[yicheng47]

Review findings:

1. Medium: resize-dragging is bypassed during PDF panel drag. In src/pages/Reader.tsx:884, the new viewer ResizeObserver calls renderer.relayout() even while the drag handler has set resize-dragging. In the bumped submodule, public/foliate-js/pdf-scroll.js:96 makes relayout() immediately run #layoutAll(), and #layoutAll() still calls onZoom for loaded pages at public/foliate-js/pdf-scroll.js:399. That defeats the drag suppression and can reintroduce PDF resize jank whenever the user pauses mid-drag. Gate relayoutPdf on !renderer.hasAttribute("resize-dragging"), or make relayout() itself respect the attribute and rely on the final removeAttribute render.

Verification:

• pnpm exec tsc --noEmit passed.
• pnpm run lint passed with existing warnings.
• node --check public/foliate-js/pdf-scroll.js passed.
• node --check public/foliate-js/fixed-layout.js passed.
• git diff --check origin/main...HEAD passed.
• git -C public/foliate-js diff --check 4f5f996be43b65c958aadeedc29d5d2e213760c1..f647a4a5cf2cc0757ac8050c40ae4c04453612c7 passed.

[yicheng47]

Addressed the review finding.

Changes:

• Reader.tsx now skips the PDF resize observer relayout while the renderer has resize-dragging.
• foliate-js PDF renderers now also make relayout() no-op during resize-dragging, relying on the final removeAttribute render after drag ends.
• Updated submodule pointer to a3c3902713ed1e0b533152804a94f43640bd504a.

Validation:

• pnpm exec tsc --noEmit
• pnpm run lint with existing warnings only
• node --check public/foliate-js/pdf-scroll.js
• node --check public/foliate-js/fixed-layout.js
• git diff --check
• git -C public/foliate-js diff --check