refactor(chat-ui): 抽离侧边栏并统一账号/实时/隐私状态

新增 SidebarRail 组件并统一主导航入口

引入 chatAccounts/chatRealtime/privacy 三个 Pinia store 复用全局状态

聊天/联系人/朋友圈页面去重侧栏逻辑，app 根布局统一承载标题栏与内容区

frontend/stores/chatAccounts.js

@@ -0,0 +1,107 @@
+import { defineStore } from 'pinia'
+
+const SELECTED_ACCOUNT_KEY = 'ui.selected_account'
+
+export const useChatAccountsStore = defineStore('chatAccounts', () => {
+  const accounts = ref([])
+  const selectedAccount = ref(null)
+  const loading = ref(false)
+  const error = ref('')
+  const loaded = ref(false)
+
+  let loadPromise = null
+
+  const readSelectedAccount = () => {
+    if (!process.client) return null
+    try {
+      const raw = localStorage.getItem(SELECTED_ACCOUNT_KEY)
+      const v = String(raw || '').trim()
+      return v || null
+    } catch {
+      return null
+    }
+  }
+
+  const writeSelectedAccount = (value) => {
+    if (!process.client) return
+    try {
+      const v = String(value || '').trim()
+      if (!v) {
+        localStorage.removeItem(SELECTED_ACCOUNT_KEY)
+        return
+      }
+      localStorage.setItem(SELECTED_ACCOUNT_KEY, v)
+    } catch {}
+  }
+
+  const setSelectedAccount = (next) => {
+    selectedAccount.value = next ? String(next) : null
+    writeSelectedAccount(selectedAccount.value)
+  }
+
+  if (process.client) {
+    watch(selectedAccount, (next) => {
+      writeSelectedAccount(next)
+    })
+  }
+
+  const ensureLoaded = async ({ force = false } = {}) => {
+    if (!process.client) return
+    if (loaded.value && !force) return
+
+    if (loadPromise && !force) {
+      await loadPromise
+      return
+    }
+
+    loadPromise = (async () => {
+      loading.value = true
+      error.value = ''
+
+      if (!selectedAccount.value) {
+        const cached = readSelectedAccount()
+        if (cached) selectedAccount.value = cached
+      }
+
+      try {
+        const api = useApi()
+        const resp = await api.listChatAccounts()
+        const nextAccounts = Array.isArray(resp?.accounts) ? resp.accounts : []
+        accounts.value = nextAccounts
+
+        const preferred = String(selectedAccount.value || '').trim()
+        const defaultAccount = String(resp?.default_account || '').trim()
+        const fallback = defaultAccount || nextAccounts[0] || ''
+        const nextSelected = preferred && nextAccounts.includes(preferred) ? preferred : (fallback || null)
+
+        selectedAccount.value = nextSelected
+        writeSelectedAccount(nextSelected)
+        loaded.value = true
+      } catch (e) {
+        accounts.value = []
+        selectedAccount.value = null
+        writeSelectedAccount(null)
+        loaded.value = true
+        error.value = e?.message || '加载账号失败'
+      } finally {
+        loading.value = false
+      }
+    })()
+
+    try {
+      await loadPromise
+    } finally {
+      loadPromise = null
+    }
+  }
+
+  return {
+    accounts,
+    selectedAccount,
+    loading,
+    error,
+    loaded,
+    ensureLoaded,
+    setSelectedAccount,
+  }
+})