feat: 重构布局与模型配置

- 写作范式分析页面改为左中右三栏布局
- 范式分段写作页面改为左中右三栏布局
- 模型设置移至设置中心，支持多服务商选择
- API 配置通过 .env 文件管理，提升安全性
- 支持 DeepSeek、OpenAI、Claude、自定义服务商

src/App.vue

@@ -19,6 +19,7 @@
         <!-- 左侧/中间配置侧边栏 -->
         <WriterPanel v-if="currentPage === 'writer'" />
         <AnalysisPanel v-else-if="currentPage === 'analysis'" />
+        <ParadigmWriterPanel v-else-if="currentPage === 'paradigmWriter'" />
         <DocumentsPanel 
           v-else-if="currentPage === 'documents'" 
           @toggle-version-panel="toggleVersionPanel"
@@ -58,6 +59,7 @@ import ComparePanel from './components/ComparePanel.vue'
 import DocumentVersionPanel from './components/DocumentVersionPanel.vue'
 import DiffAnnotationPanel from './components/DiffAnnotationPanel.vue'
 import ArticleRewritePanel from './components/ArticleRewritePanel.vue'
+import ParadigmWriterPanel from './components/ParadigmWriterPanel.vue'
 
 const appStore = useAppStore()
 const currentPage = computed(() => appStore.currentPage)