feat(message): add embedded mode to ChatScreen for desktop dual-column layout

Replace EmbeddedChat with unified ChatScreen supporting embedded mode through props. Pass conversation data, layout constraints, and navigation callbacks directly to ChatScreen instead of using separate embedded component. Consolidates dual-column layout logic into single component with conditional rendering based on isEmbedded prop.

src/stores/chatSettingsStore.ts

@@ -11,19 +11,32 @@ import { useShallow } from 'zustand/react/shallow';
 // 主题配置 - 扩展包含更多颜色
 export const CHAT_THEMES = [
   { 
-    id: 'default', 
+    id: 'white', 
+    name: '纯白', 
+    primary: '#FF6B35', 
+    secondary: '#F0F2F5', 
+    bubble: '#E8E8E8', 
+    icon: '🤍',
+    card: '#FFFFFF',
+    inputBg: '#FFFFFF',
+    panelBg: '#F5F5F5',
+    headerBg: '#FFFFFF',
+    textPrimary: '#1A1A1A',
+    textSecondary: '#666666',
+  },
+  { 
+    id: 'green', 
     name: '默认绿', 
     primary: '#4CAF50', 
     secondary: '#E8F5E9', 
     bubble: '#DCF8C6', 
     icon: '🏠',
-    // 扩展颜色
-    card: '#FFFFFF',           // 卡片背景
-    inputBg: '#FFFFFF',        // 输入框背景
-    panelBg: '#F5F5F5',        // 面板背景
-    headerBg: '#FFFFFF',       // 头部背景
-    textPrimary: '#1A1A1A',    // 主要文字
-    textSecondary: '#666666',  // 次要文字
+    card: '#FFFFFF',
+    inputBg: '#FFFFFF',
+    panelBg: '#F5F5F5',
+    headerBg: '#FFFFFF',
+    textPrimary: '#1A1A1A',
+    textSecondary: '#666666',
   },
   { 
     id: 'yellow',