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.css

@@ -283,6 +283,9 @@ input[type=range]{ width:100%; accent-color:var(--primary); }
 .bg-row .bg-name{ font-weight:600; }
 .bg-row .bg-sub{ font-size:12px; color:var(--on-surface-variant); margin-top:2px; display:flex; align-items:center; gap:6px; flex-wrap:wrap; }
 .bg-row .btn{ flex:0 0 auto; }
+.bg-group{ margin:14px 0 8px; font-weight:600; font-size:13px; color:var(--on-surface-variant); }
+.bg-group:first-of-type{ margin-top:0; }
+.bg-group + .bg-list{ margin-bottom:4px; }
 
 /* 实时屏幕（屏幕页） */
 .screen-frame{ display:flex; justify-content:center; max-width:480px; margin:0 auto; }