feat(lib): shelf sort/section pure helpers + formatSize extraction, table tests

frontend/src/lib/shelf.ts

@@ -0,0 +1,19 @@
+import type { Book } from "../api/types";
+import { groupByDir } from "./group";
+
+export type SortKey = "added" | "title" | "progress";
+export const SORT_LABEL: Record<SortKey, string> = { added: "最近入库", title: "标题", progress: "阅读进度" };
+export type GroupMode = "flat" | "dir";
+
+export function sortBooks(books: Book[], key: SortKey): Book[] {
+  const a = [...books];
+  if (key === "title") return a.sort((x, y) => x.title.localeCompare(y.title, "zh"));
+  if (key === "progress") return a.sort((x, y) => y.percent - x.percent || (x.added_at < y.added_at ? 1 : x.added_at > y.added_at ? -1 : 0));
+  return a.sort((x, y) => (x.added_at < y.added_at ? 1 : x.added_at > y.added_at ? -1 : 0));
+}
+
+/** 页面分组视图:flat 一段无标题;dir 沿用「根目录置顶、目录名 locale 排序」。 */
+export function sections(books: Book[], key: SortKey, mode: GroupMode): { label: string; books: Book[] }[] {
+  if (mode === "flat") return [{ label: "", books: sortBooks(books, key) }];
+  return groupByDir(sortBooks(books, key)).map((g) => ({ label: g.dir, books: g.books }));
+}