feat: M6.43 — reader分段流式读取(Phase1,只txt) + 面板前台管理/返回回桌面按钮

- reader分段(只txt): core/seg.{h,c} 512KB码位对齐切段(尾字完整)+manifest+按需读单段; book.c rd_book_open只布局每页所在段(治CPU100%/返回无效) load_seg只读当前段(非txt原路径); reader.c 进度实时保存(翻页/刮擦/字号/编码dirty+on_tick节流落盘+退出即时写,锚点存段号,崩溃不丢进度); rdtxt.c fread替代fgetc(去开书扫描卡顿); Phase2(双段拼接+4%释放)留待
- 面板: /api/ams/bg加fg/fg_count(后台保持向后兼容)+POST /api/ams/:pkg/killfg(前台救命:优先am kill,launcher拒则pid直信号SIGTERM->SIGKILL绕过门控)+前端/#/bg前台组'终止'绿徽标+确认弹窗(一键清仍只后台不误杀前台); POST /api/input/gesture(返回=左缘右滑/回桌面=底部上滑,注入滑动轨迹复用SDK手势)+前端屏幕控制页加返回/回桌面MD3按钮

0warning;宿主test_reader_core 72-0/seg_smoke 19-0/loaders_smoke/book_smoke/formats_smoke PASS;面板selftest/node check PASS

patch_v2/reader_app/test/book_smoke.c

@@ -31,6 +31,9 @@ int main(int argc, char **argv)
     write_txt(txt);
 
     rd_book *b = NULL;
+    /* R3.2：启用分段流式缓存（/tmp），走「切 512KB 段 + 按需布局」路径，而非全量直排 */
+    rd_book_set_seg_base("/tmp/meow_seg_smoke");
+    rd_book_set_index_dir("/tmp/meow_seg_smoke_index");
     int rc = rd_book_open(&b, txt, font, 20, 130, 480, 720, 16, 20, 62);
     CHECK(rc == 0, "rd_book_open");
     if (rc != 0) { printf("open rc=%d\n", rc); return 1; }