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/meowpanel/web/meowpanel.js

@@ -21,7 +21,7 @@ const { $, $$, LOG_GROUP_NAME, SPARK_MAX, api, apiDownload, applyTheme, authMode
     notif: { title: '通知中心', render: renderNotif, bind: bindNotif },
     power: { title: '电源 / 功耗', render: renderPower, bind: bindPower },
     proc: { title: '进程 / 服务', render: renderProc, bind: bindProc },
-    bg: { title: '后台管理', render: renderBg, bind: bindBg }
+    bg: { title: 'App 活动（前台可终止 · 后台管理）', render: renderBg, bind: bindBg }
   };
   let started = false;