feat: 自动保存/移除撤销与红点, 间隔合并改进(DAILY/稀疏/交错拆分), 删死代码, 更新测试与文档

- organize: seriesKey 移除 weekday, 解锁每3天等 DAILY 序列合并
- organize: fitSeries 放宽阈值(稀疏序列如 BUS LAW Workshop 合并)
- organize: 新增 splitIntoChains, GCD=1 的交错多班次拆为多个系列
- useCalendar: 移除 dirty/history/undo/snapshot/markSaved 死代码
- HeaderBar: 移除撤销按钮与红点●, 下载兜底序列化当前状态
- 测试: 42 项(原32), 覆盖 DAILY/稀疏/交错拆分/两两和候选等场景
- 文档: README 精简, 新增 docs/organize-algorithm.md 与 auto-save-design.md
- 保留移动端 CSS 适配

src/App.vue

@@ -68,7 +68,7 @@ body {
   align-items: center;
   gap: 24px;
 }
-.app-header h1 { font-size: 18px; font-weight: 600; }
+.app-header h1 { font-size: 18px; font-weight: 600; white-space: nowrap; }
 .view-switcher {
   display: flex;
   background: #1a252f;
@@ -91,4 +91,21 @@ body {
 }
 .app-main { flex: 1; display: flex; overflow: hidden; }
 .detail-area { flex: 1; overflow-y: auto; }
+
+/* 移动端适配 */
+@media (max-width: 768px) {
+  .app-header {
+    flex-direction: column;
+    gap: 10px;
+    padding: 10px 12px;
+  }
+  .header-left {
+    width: 100%;
+    justify-content: space-between;
+    gap: 12px;
+  }
+  .app-header h1 { font-size: 15px; }
+  .view-switcher button { padding: 5px 10px; font-size: 12px; }
+  .app-main { flex-direction: column; }
+}
 </style>