fix: stabilize Android reader scrolling

[codedogQBY]

Summary

• let Android scroll mode use native WebView/renderer scrolling instead of Foliate touch-driven page movement
• throttle scroll-mode relocate messages from the reader bridge to reduce React Native update pressure while scrolling
• throttle reader UI/context updates from relocate events so progress, chapter, and AI reading context stay current without rerendering on every scroll tick
• restore scroll renderer block sizing and native inertia settings for smoother long-page scrolling

Fixes #548
Fixes #565
Fixes #567
Fixes #571

Analysis

The 1.3.5 reports describe the same Android scroll-mode regression from different angles: sticky/short scroll distance, jumping to non-adjacent paragraphs, line/content misalignment, and occasional flicker during long reading sessions. The common path is continuous scroll relocation: Foliate was still intercepting touch movement in scrolled mode and manually mutating container position, while every relocate event immediately crossed the WebView bridge and triggered multiple React Native state/context updates. That made Android scroll feel blocked or jumpy under pressure.

Verification

• PASS: /Users/bealqiu/.cache/codex-runtimes/codex-primary-runtime/dependencies/node/bin/node packages/app-expo/scripts/build-reader.js
• PASS: git diff --cached --check
• BLOCKED: packages/app-expo/node_modules/.bin/tsc -p packages/app-expo/tsconfig.json --noEmit, existing missing packages: base64-js, @smithy/protocol-http, @smithy/querystring-builder
• BLOCKED: biome check on touched files, existing ReaderScreen lint backlog reports noExplicitAny, hook dependency diagnostics, unused variables, and related pre-existing warnings

[codedogQBY]

补充一份更细的验证 checklist，方便合并前复核：

已执行：

• PASS packages/app-expo/scripts/build-reader.js：Reader WebView bridge 构建通过，确认 reader 侧脚本改动能产出。
• PASS git diff --cached --check：无空白/补丁格式问题。

已知阻塞，不归这个 PR：

• BLOCKED packages/app-expo/node_modules/.bin/tsc -p packages/app-expo/tsconfig.json --noEmit：仓库当前缺 base64-js、@smithy/protocol-http、@smithy/querystring-builder。
• BLOCKED touched-file Biome 扩展检查：ReaderScreen.tsx 仍有既有 lint backlog，包括 noExplicitAny、hook dependency diagnostics、unused variables 等。

建议真机回归：

• Android 长篇 EPUB/PDF 连续滚动 10-15 分钟，观察是否还出现短距离卡住、跳段、闪烁。
• 分别验证滚动模式和翻页模式，确认 relocate/progress/章节高亮仍更新。
• 在阅读中打开 AI/划线/设置面板后返回，确认滚动惯性和当前阅读位置没有回退。