Update README and add MIT license

LICENSE

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+MIT License
+
+Copyright (c) 2025 CountDown
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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-# Tauri + React + Typescript
+# CountDown - 纪念日倒计时应用
 
-This template should help get you started developing with Tauri, React and Typescript in Vite.
+一个基于 Tauri + React + TypeScript 构建的跨平台纪念日倒计时应用，支持桌面端和移动端。
 
-## Recommended IDE Setup
+## ✨ 特性
 
-- [VS Code](https://code.visualstudio.com/) + [Tauri](https://marketplace.visualstudio.com/items?itemName=tauri-apps.tauri-vscode) + [rust-analyzer](https://marketplace.visualstudio.com/items?itemName=rust-lang.rust-analyzer)
+- 📅 添加和管理重要纪念日
+- ⏰ 实时计算从纪念日开始到现在的天数
+- 🎨 8种精美主题，每次启动随机切换
+- 📱 响应式设计，支持桌面和移动端
+- 🗃️ 本地SQLite数据库存储
+- ⚡ 基于Tauri的原生性能
+
+## 🎨 主题系统
+
+应用内置8种不同风格的主题：
+- 🔵 蓝色主题（默认）
+- 🟢 绿色主题
+- 🟣 紫色主题
+- 🟠 橙色主题
+- 🩷 粉色主题
+- 🔷 青色主题
+- ⚫ 暗色主题
+- 🌈 渐变主题
+
+每次启动应用会随机选择一个主题，为用户带来不同的视觉体验。
+
+## 🚀 快速开始
+
+### 环境要求
+- Node.js 18+
+- Rust 1.70+
+- pnpm
+
+### 安装依赖
+```bash
+pnpm install
+```
+
+### 开发模式
+```bash
+pnpm tauri dev
+```
+
+### 构建应用
+```bash
+# 桌面端
+pnpm tauri build
+
+# 或使用脚本
+./build_desktop.sh
+
+# Android端
+./build_android.sh
+```
+
+## 🏗️ 技术架构
+
+### 前端
+- **框架**: React 18 + TypeScript
+- **路由**: React Router DOM
+- **构建**: Vite
+- **样式**: CSS Variables + 响应式设计
+
+### 后端
+- **框架**: Tauri 2.x + Rust
+- **数据库**: SQLite (rusqlite)
+- **数据序列化**: Serde
+- **日期处理**: Chrono
+
+### 数据库结构
+```sql
+CREATE TABLE anniversaries (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    title TEXT NOT NULL,
+    start_date TEXT NOT NULL,
+    created_at DATETIME DEFAULT CURRENT_TIMESTAMP
+);
+```
+
+## 📱 功能页面
+
+应用包含三个主要页面：
+- **首页**: 显示所有纪念日列表和天数统计
+- **详情页**: 查看单个纪念日详情和删除操作
+- **添加页**: 创建新的纪念日记录
+
+## 📄 许可证
+
+本项目使用 [MIT License](LICENSE) 开源协议。