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/components/WriterPanel.vue

@@ -165,7 +165,7 @@
 
     <!-- 底部操作区 -->
     <footer class="writer-footer">
-      <div class="flex items-center justify-between">
+      <div class="flex items-center justify-between mb-3">
         <label class="flex items-center gap-2 cursor-pointer">
           <input type="checkbox" v-model="showPromptDebug" class="hidden">
           <div class="toggle-switch" :class="{'active': showPromptDebug}">
@@ -176,22 +176,6 @@
         <span class="text-xs text-muted">deepseek</span>
       </div>
 
-      <!-- API配置 -->
-      <div class="space-y-2">
-        <input
-          v-model="apiUrl"
-          type="text"
-          class="writer-input"
-          placeholder="API 地址"
-        >
-        <input
-          v-model="apiKey"
-          type="password"
-          class="writer-input"
-          placeholder="API Key"
-        >
-      </div>
-
       <button
         @click="generateContent"
         :disabled="!canGenerate"
@@ -223,8 +207,6 @@ const {
   expertGuidelines,
   isGenerating,
   showPromptDebug,
-  apiUrl,
-  apiKey,
   isDeepMode,
   inputType,
   outlinePoints