feat: 完善多账号连接诊断与聊天媒体导出

- 新增微信账号发现、环境诊断和分步数据库连接引导
- 支持按账号安全保存数据库密钥及快速切换账号
- 完善 WCDB 历史消息分片读取和分页状态提示
- 支持导出图片、视频和语音，提供原图优先及缩略图回退
- 更新安装指引、兼容版本说明和相关自动化测试

src/main/services/account-discovery.ts

@@ -0,0 +1,58 @@
+import crypto from 'crypto'
+import fs from 'fs-extra'
+import path from 'path'
+import type { AccountDiscoveryResult, WechatAccountCandidate } from '../../shared/database-key'
+import { DatabaseKeyStore } from '../database-key-store'
+import { getBootstrapCache } from './bootstrap-cache'
+import { validateDbRoot } from './settings-store'
+
+function accountId(accountRoot: string): string {
+  return crypto.createHash('sha256').update(path.resolve(accountRoot).toLowerCase()).digest('hex')
+}
+
+export async function discoverAccounts(
+  inputPath: string,
+  keyStore: DatabaseKeyStore,
+  currentAccountRoot?: string
+): Promise<AccountDiscoveryResult> {
+  const validation = validateDbRoot(inputPath)
+  if (!validation.valid) return { success: false, accounts: [], error: validation.error }
+
+  const normalizedInput = path.resolve(inputPath)
+  const isAccount = await fs.pathExists(path.join(normalizedInput, 'db_storage'))
+  const roots = isAccount
+    ? [normalizedInput]
+    : (await fs.readdir(normalizedInput, { withFileTypes: true }))
+        .filter((entry) => entry.isDirectory())
+        .map((entry) => path.join(normalizedInput, entry.name))
+        .filter((candidate) => fs.existsSync(path.join(candidate, 'db_storage')))
+
+  const accounts: WechatAccountCandidate[] = await Promise.all(
+    roots.map(async (accountRoot) => {
+      const cached = getBootstrapCache(accountRoot)?.self
+      return {
+        id: accountId(accountRoot),
+        accountRoot,
+        directoryName: path.basename(accountRoot),
+        wxid: cached?.wxid,
+        nickname: cached?.nickname,
+        avatar: cached?.avatar,
+        hasSavedDbKey: (await keyStore.getStatus(accountRoot)).saved,
+        loginStatus: currentAccountRoot
+          ? path.resolve(currentAccountRoot).toLowerCase() ===
+            path.resolve(accountRoot).toLowerCase()
+            ? 'current'
+            : 'other'
+          : 'unknown',
+        selectedByInput: isAccount
+      }
+    })
+  )
+
+  return {
+    success: true,
+    inputKind: isAccount ? 'account' : 'root',
+    accounts,
+    preselectedAccountId: isAccount ? accounts[0]?.id : undefined
+  }
+}

src/main/services/connection-diagnostics.ts

@@ -0,0 +1,69 @@
+import { execFile } from 'child_process'
+import fs from 'fs-extra'
+import os from 'os'
+import path from 'path'
+import { promisify } from 'util'
+import { isUsableDbRoot } from './settings-store'
+
+const execFileAsync = promisify(execFile)
+
+const platformLabel = (): string => {
+  if (process.platform === 'win32') return `Windows ${os.release()} (${process.arch})`
+  if (process.platform === 'darwin') return `macOS ${os.release()} (${process.arch})`
+  return `${process.platform} ${os.release()} (${process.arch})`
+}
+
+async function detectWindowsWechatVersion(): Promise<string> {
+  const script = [
+    '$process = Get-Process Weixin,WeChat -ErrorAction SilentlyContinue | Where-Object Path | Select-Object -First 1',
+    '$candidate = if ($process) { $process.Path } else {',
+    "  @($env:ProgramFiles, ${env:ProgramFiles(x86)}) | Where-Object { $_ } | ForEach-Object { Join-Path $_ 'Tencent\\WeChat\\WeChat.exe' } | Where-Object { Test-Path $_ } | Select-Object -First 1",
+    '}',
+    'if ($candidate) { (Get-Item -LiteralPath $candidate).VersionInfo.ProductVersion }'
+  ].join('; ')
+  try {
+    const { stdout } = await execFileAsync(
+      'powershell.exe',
+      ['-NoProfile', '-NonInteractive', '-Command', script],
+      { timeout: 3000, windowsHide: true }
+    )
+    return stdout.trim() || '未检测到'
+  } catch {
+    return '未检测到'
+  }
+}
+
+async function detectMacWechatVersion(): Promise<string> {
+  const candidates = [
+    '/Applications/WeChat.app/Contents/Info',
+    path.join(os.homedir(), 'Applications/WeChat.app/Contents/Info')
+  ]
+  for (const candidate of candidates) {
+    if (!fs.existsSync(`${candidate}.plist`)) continue
+    try {
+      const { stdout } = await execFileAsync(
+        '/usr/bin/defaults',
+        ['read', candidate, 'CFBundleShortVersionString'],
+        { timeout: 3000 }
+      )
+      if (stdout.trim()) return stdout.trim()
+    } catch {
+      // Continue to the next known installation location.
+    }
+  }
+  return '未检测到'
+}
+
+export async function detectWechatVersion(): Promise<string> {
+  if (process.platform === 'win32') return detectWindowsWechatVersion()
+  if (process.platform === 'darwin') return detectMacWechatVersion()
+  return '未检测到'
+}
+
+export function detectDataStructureVersion(dbRoot: string): string {
+  return isUsableDbRoot(dbRoot) ? '微信 4.x（WCDB）' : '未检测到'
+}
+
+export function getOsVersionLabel(): string {
+  return platformLabel()
+}

src/main/services/settings-store.ts

@@ -86,7 +86,7 @@ function unique(values: string[]): string[] {
   return Array.from(new Set(values))
 }
 
-function isUsableDbRoot(candidate?: string): boolean {
+export function isUsableDbRoot(candidate?: string): boolean {
   if (!candidate || !fs.existsSync(candidate)) return false
   if (fs.existsSync(path.join(candidate, 'db_storage'))) return true
   try {
@@ -98,6 +98,21 @@ function isUsableDbRoot(candidate?: string): boolean {
   }
 }
 
+export function validateDbRoot(candidate?: string): { valid: boolean; error?: string } {
+  const root = String(candidate || '').trim()
+  if (!root) return { valid: false, error: '微信数据目录为空，请重新选择目录' }
+  if (!fs.existsSync(root)) {
+    return { valid: false, error: '微信数据目录不存在，请检查路径或重新选择目录' }
+  }
+  if (!isUsableDbRoot(root)) {
+    return {
+      valid: false,
+      error: '所选目录中未找到微信 4.x 数据库（db_storage），请选择 xwechat_files 或账号目录'
+    }
+  }
+  return { valid: true }
+}
+
 const defaultDbRoot = getDefaultDbRoot()
 
 const DEFAULT_SETTINGS: AppSettings = {