fix(cbz): smooth scrollbar/slider dragging — rAF-coalesce scroll handler, idle-debounced prefetch, frame-batched height corrections, PageHeights.setEst converges unseen pages to the first measured page size, page slider seeks instantly while scrubbing (no per-notch smooth-animation restart); restore lost ### Fixed header in changelog

docs/CHANGELOG_web.md

@@ -24,6 +24,10 @@ The format loosely follows Keep a Changelog and can be adapted to the team's hab
 - Whole UI restyled to a warm library palette (stone surfaces + amber accents, replacing cool zinc + emerald): warmer dark chrome, amber primary buttons/links, hover/press feedback on shelf cards (cover lift + glow), reader header with format badge and blur, pill-style CBZ page indicator, EPUB spread centered like a book page.
 - 全站换为暖色「书房」配色（stone 深灰面 + amber 琥珀强调，替代冷色 zinc + emerald）：书架封面悬停上浮高亮、阅读器顶栏带格式徽章与毛玻璃、CBZ 页码改为悬浮胶囊、EPUB 页面居中成书卷感，主按钮/链接统一琥珀色并补齐悬停/焦点反馈。
 
+### Fixed / 修复
+
+- Dragging the comic scrollbar (or the page slider) is no longer gritty: scroll handling is coalesced to one update per frame instead of per event, prefetching waits until scrolling settles instead of firing mid-drag, height corrections are batched per frame, the virtual list re-estimates unseen pages from the first measured page size (scrollbar geometry stops morphing under your finger), and slider seeks land instantly instead of restarting a smooth-scroll animation per notch.
+- 漫画拖动滚动条(及页码滑条)不再发涩:滚动改为每帧合并处理而非逐事件响应,预取等滚动停稳再发(不再拖拽途中抢带宽),量高补偿按帧合并,虚拟列表用首个实测页高重估所有未加载页(滚动条几何不再拖拽中变形),滑条寻址即时落位(不再每格重启一段平滑动画)。
 - .txt/.md files encoded in GBK/GB2312/GB18030 or UTF-16 (typical web-novel exports) no longer render as mojibake: the reader strictly tries UTF-8 first and falls back to GB18030, recognizing UTF-16 by BOM.
 - GBK/GB2312/GB18030 或 UTF-16 编码的 .txt/.md（网文导出常见）不再乱码：阅读器先按 UTF-8 严格解码，失败自动回退 GB18030，UTF-16 靠 BOM 识别。
 - Reading a large .txt no longer freezes the browser: the text is split into chapters (「第X章」/Chapter X/序章… markers, pseudo-sections for unmarked files) and rendered one chapter at a time with a chapter selector and prev/next navigation; 「第X卷/部」 are volume groupings (dropdown optgroups), not chapter breaks, and books with only volumes split by volume; reading progress restores to the saved chapter.