feat: 合并星图和聊天页面为 MainPage，响应式 GridRow 布局

- 新建 MainPage.ets，用 GridRow 响应式布局组合星图+聊天
- Index.ets 改为 2 Tab（TrulyMEM + 设置）
- GraphPage/ChatPage 接收 @Prop db 从父组件传入
- 恢复 README.md / README_EN.md 的特别鸣谢部分

harmonyos/oh-package.json5

@@ -1,7 +1,8 @@
 {
   "modelVersion": "5.0.5",
-  "description": "TrulyMEM - True Memory Engine for HarmonyOS",
-  "dependencies": {},
+  "description": "Please describe the basic information.",
+  "dependencies": {
+  },
   "devDependencies": {
     "@ohos/hypium": "1.0.24",
     "@ohos/hamock": "1.0.0"