feat(reader): immersive chrome + WeChat-Read/Mihon-style bottom sheets — tap-center toggles header/toolbar, progress & page sliders seek anywhere, WYSIWYG theme swatches, A± font size; CBZ gains 连读/整页/适高 modes, edge-tap & arrow-key paging, persisted mode (seekChapter helper + test)

frontend/src/lib/chapters.ts

@@ -47,3 +47,10 @@ export function splitChapters(text: string): TxtChapter[] {
 export function chapterText(text: string, chapters: TxtChapter[], i: number): string {
   return text.slice(chapters[i].start, chapters[i + 1]?.start ?? text.length);
 }
+
+/** 全书进度分数(0..1)→ 章序号 + 章内分数。进度滑条用。 */
+export function seekChapter(n: number, frac: number): { idx: number; intra: number } {
+  const p = Math.min(0.9999, Math.max(0, frac)) * n;
+  const idx = Math.min(n - 1, Math.floor(p));
+  return { idx, intra: p - idx };
+}

frontend/src/lib/readerPrefs.ts

@@ -28,8 +28,7 @@ export function useReaderPrefs() {
   return {
     prefs,
     fontSize: FONT_SIZES[prefs.sizeIdx],
-    cycleTheme: () =>
-      setPrefs((p) => ({ ...p, theme: RD_THEMES[(RD_THEMES.indexOf(p.theme) + 1) % RD_THEMES.length] })),
+    setTheme: (theme: RdTheme) => setPrefs((p) => ({ ...p, theme })),
     bump: (d: number) =>
       setPrefs((p) => ({ ...p, sizeIdx: Math.min(FONT_SIZES.length - 1, Math.max(0, p.sizeIdx + d)) })),
   };

frontend/src/lib/useProgress.ts

@@ -4,9 +4,16 @@ import { api } from "../api/client";
 import type { Book } from "../api/types";
 import { createProgressSaver, type ProgressSaver } from "./progress";
 
+export interface Chrome {
+  on: boolean;
+  toggle(): void;
+  show(): void;
+}
+
 export interface ReaderProps {
   book: Book;
   initialLocator?: Record<string, unknown>;
+  chrome: Chrome;
 }
 
 export function useProgressSaver(bookId: number): ProgressSaver {