feat: Features架构迁移 - P0和P1部分完成

## 完成的工作

### P0: 基础设施准备
- 创建 features/ 和 shared/ 目录结构
- 迁移共享资源：API基础设施、工具函数、类型定义
- 迁移通用composables：useMoney, useSmsCountdown, usePricingCalculator
- 迁移全局样式文件
- 建立模块化导出系统

### P1.1: 钱包模块 (wallet)
- 迁移 API: wallet.ts
- 迁移 Views: WalletView.vue
- 新增 Composable: useWallet.ts (封装钱包状态管理)
- 更新导入路径到 shared/

### P1.2: 聊天模块 (chats)
- 迁移 API: chats.ts
- 迁移 Views: ChatView, MessagesView (桌面+移动)
- 迁移 Composables: useChatSSE.ts
- 迁移 Components: ChatAttachmentImage.vue
- 更新导入路径到 shared/

## 技术改进
- 修复 shared/composables 导出问题 (default → 命名导出)
- 修复 shared/api/client.ts 类型导入路径
- 建立清晰的模块边界和导出规范

## 文档
- 添加完整的迁移计划文档
- 添加进度跟踪文档

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/features/wallet/composables/useWallet.ts

@@ -0,0 +1,54 @@
+import { ref, computed } from 'vue'
+import { fetchWalletBalance, fetchWalletLedger } from '../api/wallet'
+import type { WalletAccount, WalletLedger } from '../api/wallet'
+
+export function useWallet() {
+  const balance = ref<WalletAccount | null>(null)
+  const ledgers = ref<WalletLedger[]>([])
+  const loading = ref(false)
+  const error = ref<string | null>(null)
+
+  const availableBalance = computed(() => balance.value?.available_balance ?? 0)
+  const frozenBalance = computed(() => balance.value?.frozen_balance ?? 0)
+  const totalBalance = computed(() => availableBalance.value + frozenBalance.value)
+
+  async function loadBalance() {
+    loading.value = true
+    error.value = null
+    try {
+      balance.value = await fetchWalletBalance()
+    } catch (err) {
+      error.value = err instanceof Error ? err.message : '加载余额失败'
+      throw err
+    } finally {
+      loading.value = false
+    }
+  }
+
+  async function loadLedger(page = 1, pageSize = 20) {
+    loading.value = true
+    error.value = null
+    try {
+      const result = await fetchWalletLedger(page, pageSize)
+      ledgers.value = result.items
+      return result
+    } catch (err) {
+      error.value = err instanceof Error ? err.message : '加载账单失败'
+      throw err
+    } finally {
+      loading.value = false
+    }
+  }
+
+  return {
+    balance,
+    ledgers,
+    loading,
+    error,
+    availableBalance,
+    frozenBalance,
+    totalBalance,
+    loadBalance,
+    loadLedger,
+  }
+}