feat: 新增 claude-sonnet-4-6 模型支持

- 后端默认映射、身份注入、迁移文件
- 前端模型列表和快捷映射按钮

frontend/src/composables/useModelWhitelist.ts

@@ -60,6 +60,7 @@ const antigravityModels = [
   // Claude 4.5+ 系列
   'claude-opus-4-6',
   'claude-opus-4-5-thinking',
+  'claude-sonnet-4-6',
   'claude-sonnet-4-5',
   'claude-sonnet-4-5-thinking',
   // Gemini 2.5 系列
@@ -271,6 +272,7 @@ const antigravityPresetMappings = [
   { label: 'Gemini 3→Flash', from: 'gemini-3*', to: 'gemini-3-flash', color: 'bg-amber-100 text-amber-700 hover:bg-amber-200 dark:bg-amber-900/30 dark:text-amber-400' },
   { label: 'Gemini 2.5→Flash', from: 'gemini-2.5*', to: 'gemini-2.5-flash', color: 'bg-orange-100 text-orange-700 hover:bg-orange-200 dark:bg-orange-900/30 dark:text-orange-400' },
   // 精确映射
+  { label: 'Sonnet 4.6', from: 'claude-sonnet-4-6', to: 'claude-sonnet-4-6', color: 'bg-cyan-100 text-cyan-700 hover:bg-cyan-200 dark:bg-cyan-900/30 dark:text-cyan-400' },
   { label: 'Sonnet 4.5', from: 'claude-sonnet-4-5', to: 'claude-sonnet-4-5', color: 'bg-cyan-100 text-cyan-700 hover:bg-cyan-200 dark:bg-cyan-900/30 dark:text-cyan-400' },
   { label: 'Opus 4.6-thinking', from: 'claude-opus-4-6-thinking', to: 'claude-opus-4-6-thinking', color: 'bg-pink-100 text-pink-700 hover:bg-pink-200 dark:bg-pink-900/30 dark:text-pink-400' }
 ]