style: 移除 emoji, 注释改为中文 (保留专业名词)

- 移除所有 Vue 组件和 README 中的 emoji (按钮文字、标题、功能列表)
- 将 src 下所有英文注释改为中文, 保留专业名词 (RRULE, EXDATE, ICS 等)
- 涉及文件: date.js, event-factory.js, ical-io.js, organize.js,
  recur.js, split.js, weekday.js, useCalendar.js, EventDetail.vue,
  App.vue, DropZone.vue, EventList.vue, HeaderBar.vue, README.md

src/composables/useCalendar.js

@@ -6,7 +6,7 @@ import { splitRecurringEvent } from '../lib/split.js'
 
 const MAX_HISTORY = 50
 
-// Singleton reactive state
+// 单例响应式状态
 const state = reactive({
   meta: null,
   events: [],
@@ -18,7 +18,7 @@ const state = reactive({
 })
 
 // ------------------------------------------------------------------ //
-// Snapshot / undo
+// 快照 / 撤销
 // ------------------------------------------------------------------ //
 function snapshot() {
   return {
@@ -41,7 +41,7 @@ function restore(snap) {
 }
 
 // ------------------------------------------------------------------ //
-// Actions
+// 操作
 // ------------------------------------------------------------------ //
 function loadFile(file) {
   return file.text().then((text) => {
@@ -143,7 +143,7 @@ function markSaved() {
 }
 
 // ------------------------------------------------------------------ //
-// Computed
+// 计算属性
 // ------------------------------------------------------------------ //
 const selectedEvent = computed(() =>
   state.events.find((e) => e.uid === state.selectedUid) || null,