refactor(ui): 重组 composables 目录结构并优化模式功能

**目录结构重构**：
- 将 41 个 composables 文件按功能分类到 10 个子目录
- model/ - 模型管理相关（5个文件）
- prompt/ - 提示词相关（6个文件）
- context/ - 上下文相关（2个文件）
- image/ - 图像相关（2个文件）
- ui/ - UI交互相关（11个文件）
- accessibility/ - 无障碍相关（3个文件）
- performance/ - 性能优化相关（4个文件）
- storage/ - 存储相关（3个文件）
- system/ - 系统相关（2个文件）
- mode/ - 功能模式相关（4个文件）

**技术实现**：
- 使用 git mv 保留文件历史
- 为每个子目录创建 barrel export (index.ts)
- 更新 120+ 处导入路径引用
- 修复测试文件中的导入路径

**功能优化**：
- 新增 useCurrentMode composable 提供只读模式访问
- 基础模式下隐藏变量相关UI组件
- 优化 TestAreaPanel 根据功能模式动态显示变量表单

**影响范围**：
- 移动文件：41个 composables
- 新增文件：10个 index.ts
- 更新导入：120+ 处导入路径
- 测试修复：3个测试文件路径更新

Author: linshenkx

packages/ui/src/components/BasicTestMode.vue

@@ -149,7 +149,7 @@ import { ref, computed, watch, nextTick } from 'vue'
 
 import { useI18n } from 'vue-i18n'
 import { NButton, NCard } from 'naive-ui'
-import { useToast } from '../composables/useToast'
+import { useToast } from '../composables/ui/useToast'
 import type { AppServices } from '../types/services'
 import InputPanelUI from './InputPanel.vue'
 import ModelSelectUI from './ModelSelect.vue'

packages/ui/src/components/BuiltinTemplateLanguageSwitch.vue

@@ -31,7 +31,7 @@ import { ref, onMounted, computed, inject, type Ref } from 'vue'
 
 import { useI18n } from 'vue-i18n'
 import { NButton } from 'naive-ui'
-import { useToast } from '../composables/useToast'
+import { useToast } from '../composables/ui/useToast'
 import type { BuiltinTemplateLanguage } from '@prompt-optimizer/core'
 import type { AppServices } from '../types/services'
 

packages/ui/src/components/CategoryManager.vue

@@ -152,7 +152,7 @@ import {
   Plus,
   Folder
 } from '@vicons/tabler';
-import { useToast } from '../composables/useToast';
+import { useToast } from '../composables/ui/useToast';
 import { useI18n } from 'vue-i18n';
 import type { FavoriteCategory } from '@prompt-optimizer/core';
 import type { AppServices } from '../types/services';

packages/ui/src/components/DataManager.vue

@@ -187,7 +187,7 @@ import {
   NModal, NSpace, NText, NButton, NUpload, NUploadDragger, 
   NIcon, NAlert, type UploadFileInfo 
 } from 'naive-ui'
-import { useToast } from '../composables/useToast'
+import { useToast } from '../composables/ui/useToast'
 import type { AppServices } from '../types/services'
 
 interface Props {

packages/ui/src/components/FavoriteButton.vue

@@ -105,7 +105,7 @@ import {
   type FormInst,
   type FormRules
 } from 'naive-ui';
-import { useToast } from '../composables/useToast';
+import { useToast } from '../composables/ui/useToast';
 import { StarFilled, StarOutline } from '@vicons/tabler';
 import type { FavoriteCategory } from '@prompt-optimizer/core';
 import type { AppServices } from '../types/services';

packages/ui/src/components/FavoriteCard.vue

@@ -285,7 +285,7 @@ import {
 } from '@vicons/tabler';
 import { useI18n } from 'vue-i18n';
 import type { FavoritePrompt, FavoriteCategory } from '@prompt-optimizer/core';
-import { useTooltipTheme } from '../composables/useTooltipTheme';
+import { useTooltipTheme } from '../composables/ui/useTooltipTheme';
 
 const { t } = useI18n();
 

packages/ui/src/components/FavoriteManager.vue

@@ -267,8 +267,8 @@ import {
   type UploadChangeParam
 } from 'naive-ui';
 import { useI18n } from 'vue-i18n';
-import { useToast } from '../composables/useToast';
-import { useFavoriteInitializer } from '../composables/useFavoriteInitializer';
+import { useToast } from '../composables/ui/useToast';
+import { useFavoriteInitializer } from '../composables/storage/useFavoriteInitializer';
 import ToastUI from './Toast.vue';
 
 const { t } = useI18n();

packages/ui/src/components/HistoryDrawer.vue

@@ -188,7 +188,7 @@ import {
   NDivider, NCollapse, NCollapseItem, NEmpty
 } from 'naive-ui'
 import type { PromptRecord, PromptRecordChain } from '@prompt-optimizer/core'
-import { useToast } from '../composables/useToast'
+import { useToast } from '../composables/ui/useToast'
 
 const props = defineProps({
   show: Boolean,

packages/ui/src/components/ImageModelEditModal.vue

@@ -220,8 +220,8 @@ import {
   NCheckbox, NSelect, NButton, NTag, NTooltip, NText,
   NDivider, NH4, NForm, NFormItem, NImage
 } from 'naive-ui'
-import { useImageModelManager } from '../composables/useImageModelManager'
-import { useToast } from '../composables/useToast'
+import { useImageModelManager } from '../composables/model/useImageModelManager'
+import { useToast } from '../composables/ui/useToast'
 import type { ImageModelConfig } from '@prompt-optimizer/core'
 import ModelAdvancedSection from './ModelAdvancedSection.vue'
 

packages/ui/src/components/ImageModelManager.vue

@@ -145,8 +145,8 @@ import { useI18n } from 'vue-i18n'
 import {
   NSpace, NCard, NText, NTag, NButton, NEmpty, NImage
 } from 'naive-ui'
-import { useImageModelManager } from '../composables/useImageModelManager'
-import { useToast } from '../composables/useToast'
+import { useImageModelManager } from '../composables/model/useImageModelManager'
+import { useToast } from '../composables/ui/useToast'
 import type { IImageService } from '@prompt-optimizer/core'
 
 const { t } = useI18n()