perf(reader): M30 删掉无人消费的下一页预取槽（refill 渲染减半、常驻 −0.69MB）+ 回书架置顶刚读完的书

patch_v2/reader_app/app/shelf_model.c

@@ -62,6 +62,13 @@ static int cmp_recent_then_name(const void *a, const void *b)
     return strcasecmp(x->title, y->title);
 }
 
+/* 最近阅读排序（扫描后 / 刚读完置顶共用同一口径）。 */
+void shelf_sort_recent(shelf_book *books, int nbooks)
+{
+    if (!books || nbooks < 2) return;
+    qsort(books, (size_t)nbooks, sizeof(shelf_book), cmp_recent_then_name);
+}
+
 typedef struct scan_ctx {
     shelf_book    *books;
     int            cap;
@@ -177,7 +184,7 @@ int shelf_scan_books(const char *root, shelf_book *books, int cap,
     scan_ctx c;
     c.books = books; c.cap = cap; c.n = 0; c.truncated = 0; c.depth_skipped = 0; c.ts_fn = ts_fn;
     scan_dir(&c, root, 0, "", "");
-    qsort(books, (size_t)c.n, sizeof(shelf_book), cmp_recent_then_name);
+    shelf_sort_recent(books, c.n);
     if (rep) {
         rep->nbooks = c.n;
         rep->truncated = c.truncated;