feat(hooks): useSettings 添加 fontSize 支持

- Settings 接口新增 fontSize 属性
- 默认设置中添加 fontSize: 15

src/hooks/useSettings.ts

@@ -11,6 +11,7 @@ export interface Settings {
   temperature: string;
   theme: string;
   language: string;
+  fontSize: number;
   enableThinking: boolean;
   saveChatHistory: boolean;
 }
@@ -53,6 +54,7 @@ const defaultSettings: Settings = {
   temperature: '0.7',
   theme: 'light',
   language: 'zh-CN',
+  fontSize: 15,
   enableThinking: false,
   saveChatHistory: true,
 };