fix: 性能优化、前端转写器配置、任务进度丢失及 MLX Whisper 回退问题修复

### 性能优化
- 后端任务执行从串行锁改为 ThreadPoolExecutor 并发执行（默认3线程）
- 添加 GZipMiddleware 响应压缩 + Nginx gzip 配置
- 数据库连接池参数优化（pool_size=10, max_overflow=20）
- 视频帧提取并行化（ThreadPoolExecutor）
- LLM 重试配置缓存到实例，避免每次请求读 env var
- 前端路由级代码拆分（React.lazy + Suspense）
- Vite manualChunks 拆分 markdown/markmap/vendor
- MarkdownViewer 用 React.memo + useMemo 减少不必要渲染
- NoteHistory Fuse.js 实例 useMemo 缓存
- useTaskPolling 无待处理任务时跳过轮询
- 移除 antd 依赖（NoteForm Alert、modelForm Tag），改用 shadcn/ui

### 前端转写器配置（新功能）
- 新增 TranscriberConfigManager（JSON 文件存储，替代环境变量）
- 新增 GET/POST /transcriber_config API 端点
- 新增 GET /transcriber_models_status 模型下载状态查询
- 新增 POST /transcriber_download 后台模型下载触发
- 前端转写器设置页面：引擎选择、模型大小选择、模型下载管理
- deploy_status 端点同步从配置文件读取

### Bug 修复
- 修复任务进行中切换页面后进度丢失：Home.tsx status 派生逻辑补全中间状态
- 修复 MLX Whisper 静默回退 fast-whisper：移除环境变量门控，macOS 下自动尝试导入
- MLX Whisper 不可用时抛出 RuntimeError 而非静默回退
- 前端展示 MLX Whisper 可用性状态，不可用时禁用保存

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

BillNote_frontend/src/pages/SettingPage/Menu.tsx

@@ -1,5 +1,6 @@
 import {
   BotMessageSquare,
+  Captions,
   HardDriveDownload,
   Info,
   Activity,
@@ -14,14 +15,12 @@ const Menu = () => {
       icon: <BotMessageSquare />,
       path: '/settings/model',
     },
-    // TODO ：下一版本升级优化
-    // {
-    //   id: ' transcriber',
-    //   name: '音频转译配置',
-    //   icon: <Captions />,
-    //   path: '/settings/transcriber',
-    // },
-    // //下载配置
+    {
+      id: 'transcriber',
+      name: '音频转写配置',
+      icon: <Captions />,
+      path: '/settings/transcriber',
+    },
     {
       id: 'download',
       name: '下载配置',

BillNote_frontend/src/pages/SettingPage/transcriber.tsx

@@ -1,8 +1,255 @@
-const Transcriber = () => {
+import { useState, useEffect, useCallback } from 'react'
+import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card'
+import { Button } from '@/components/ui/button'
+import { Badge } from '@/components/ui/badge'
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from '@/components/ui/select'
+import { Alert, AlertDescription } from '@/components/ui/alert'
+import { AudioLines, AlertTriangle, CheckCircle2, Download, Loader2, Save, XCircle } from 'lucide-react'
+import { toast } from 'react-hot-toast'
+import {
+  getTranscriberConfig,
+  updateTranscriberConfig,
+  getModelsStatus,
+  downloadModel,
+  TranscriberConfig,
+  ModelStatus,
+} from '@/services/transcriber'
+
+const isWhisperType = (type: string) =>
+  type === 'fast-whisper' || type === 'mlx-whisper'
+
+export default function Transcriber() {
+  const [config, setConfig] = useState<TranscriberConfig | null>(null)
+  const [loading, setLoading] = useState(true)
+  const [saving, setSaving] = useState(false)
+  const [selectedType, setSelectedType] = useState('')
+  const [selectedModelSize, setSelectedModelSize] = useState('')
+  const [modelStatuses, setModelStatuses] = useState<ModelStatus[]>([])
+  const [mlxModelStatuses, setMlxModelStatuses] = useState<ModelStatus[]>([])
+  const [mlxAvailable, setMlxAvailable] = useState(false)
+
+  const fetchModelsStatus = useCallback(async () => {
+    try {
+      const data = await getModelsStatus()
+      setModelStatuses(data.whisper)
+      setMlxModelStatuses(data.mlx_whisper)
+      setMlxAvailable(data.mlx_available)
+    } catch {
+      // 静默失败，不阻塞主流程
+    }
+  }, [])
+
+  useEffect(() => {
+    const load = async () => {
+      try {
+        const data = await getTranscriberConfig()
+        setConfig(data)
+        setSelectedType(data.transcriber_type)
+        setSelectedModelSize(data.whisper_model_size)
+      } catch {
+        toast.error('获取转写器配置失败')
+      } finally {
+        setLoading(false)
+      }
+    }
+    load()
+    fetchModelsStatus()
+  }, [fetchModelsStatus])
+
+  // 有下载中的模型时自动轮询状态
+  useEffect(() => {
+    const hasDownloading =
+      modelStatuses.some(m => m.downloading) || mlxModelStatuses.some(m => m.downloading)
+    if (!hasDownloading) return
+
+    const timer = setInterval(fetchModelsStatus, 3000)
+    return () => clearInterval(timer)
+  }, [modelStatuses, mlxModelStatuses, fetchModelsStatus])
+
+  const handleSave = async () => {
+    setSaving(true)
+    try {
+      const payload: { transcriber_type: string; whisper_model_size?: string } = {
+        transcriber_type: selectedType,
+      }
+      if (isWhisperType(selectedType)) {
+        payload.whisper_model_size = selectedModelSize
+      }
+      await updateTranscriberConfig(payload)
+      toast.success('转写器配置已保存')
+    } catch {
+      toast.error('保存失败')
+    } finally {
+      setSaving(false)
+    }
+  }
+
+  const handleDownload = async (modelSize: string, transcriberType: string) => {
+    try {
+      await downloadModel({ model_size: modelSize, transcriber_type: transcriberType })
+      toast.success(`模型 ${modelSize} 开始下载`)
+      // 立即刷新状态
+      setTimeout(fetchModelsStatus, 1000)
+    } catch {
+      toast.error('下载请求失败')
+    }
+  }
+
+  if (loading) {
+    return (
+      <div className="flex h-64 items-center justify-center">
+        <Loader2 className="h-6 w-6 animate-spin text-neutral-400" />
+      </div>
+    )
+  }
+
+  if (!config) {
+    return <div className="p-6 text-center text-neutral-500">无法加载配置</div>
+  }
+
+  const currentModels = selectedType === 'mlx-whisper' ? mlxModelStatuses : modelStatuses
+
   return (
-    <div className="flex h-screen w-full flex-col items-center justify-center">
-      <h1 className="text-center text-4xl font-bold">Transcriber is under development</h1>
+    <div className="space-y-6 p-6">
+      <div>
+        <h2 className="text-2xl font-semibold">音频转写配置</h2>
+        <p className="mt-1 text-sm text-neutral-500">
+          选择视频音频转写为文字所使用的引擎，保存后对新任务立即生效
+        </p>
+      </div>
+
+      {/* 转写引擎选择 */}
+      <Card>
+        <CardHeader>
+          <CardTitle className="flex items-center gap-2 text-lg">
+            <AudioLines className="h-5 w-5" />
+            转写引擎
+          </CardTitle>
+        </CardHeader>
+        <CardContent className="space-y-4">
+          <div className="space-y-2">
+            <label className="text-sm font-medium">转写器类型</label>
+            <Select value={selectedType} onValueChange={setSelectedType}>
+              <SelectTrigger className="w-full max-w-xs">
+                <SelectValue />
+              </SelectTrigger>
+              <SelectContent>
+                {config.available_types.map(t => (
+                  <SelectItem key={t.value} value={t.value}>
+                    {t.label}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+
+          {isWhisperType(selectedType) && (
+            <div className="space-y-2">
+              <label className="text-sm font-medium">Whisper 模型大小</label>
+              <Select value={selectedModelSize} onValueChange={setSelectedModelSize}>
+                <SelectTrigger className="w-full max-w-xs">
+                  <SelectValue />
+                </SelectTrigger>
+                <SelectContent>
+                  {config.whisper_model_sizes.map(size => {
+                    const status = currentModels.find(m => m.model_size === size)
+                    return (
+                      <SelectItem key={size} value={size}>
+                        <span className="flex items-center gap-2">
+                          {size}
+                          {status?.downloaded && (
+                            <CheckCircle2 className="h-3 w-3 text-green-500" />
+                          )}
+                        </span>
+                      </SelectItem>
+                    )
+                  })}
+                </SelectContent>
+              </Select>
+              <p className="text-xs text-neutral-400">
+                模型越大精度越高，但速度更慢、占用更多显存
+              </p>
+            </div>
+          )}
+
+          {selectedType === 'mlx-whisper' && !config.mlx_whisper_available && (
+            <Alert variant="warning" className="text-sm">
+              <AlertTriangle className="h-4 w-4" />
+              <AlertDescription>
+                MLX Whisper 当前不可用。需要 macOS 平台并安装{' '}
+                <code className="rounded bg-neutral-100 px-1">pip install mlx_whisper</code>，
+                安装后重启后端生效。
+              </AlertDescription>
+            </Alert>
+          )}
+
+          <Button onClick={handleSave} disabled={saving || (selectedType === 'mlx-whisper' && !config.mlx_whisper_available)} className="mt-2">
+            {saving ? (
+              <Loader2 className="mr-2 h-4 w-4 animate-spin" />
+            ) : (
+              <Save className="mr-2 h-4 w-4" />
+            )}
+            保存配置
+          </Button>
+        </CardContent>
+      </Card>
+
+      {/* Whisper 模型管理 */}
+      {isWhisperType(selectedType) && currentModels.length > 0 && (
+        <Card>
+          <CardHeader>
+            <CardTitle className="flex items-center gap-2 text-lg">
+              <Download className="h-5 w-5" />
+              模型管理
+              <span className="text-sm font-normal text-neutral-400">
+                {selectedType === 'mlx-whisper' ? 'MLX Whisper' : 'Faster Whisper'}
+              </span>
+            </CardTitle>
+          </CardHeader>
+          <CardContent>
+            <div className="space-y-3">
+              {currentModels.map(model => (
+                <div
+                  key={model.model_size}
+                  className="flex items-center justify-between rounded-md border px-4 py-3"
+                >
+                  <div className="flex items-center gap-3">
+                    <span className="font-medium">{model.model_size}</span>
+                    {model.downloaded ? (
+                      <Badge variant="default" className="bg-green-500 hover:bg-green-600">
+                        已下载
+                      </Badge>
+                    ) : model.downloading ? (
+                      <Badge variant="secondary" className="flex items-center gap-1">
+                        <Loader2 className="h-3 w-3 animate-spin" />
+                        下载中
+                      </Badge>
+                    ) : (
+                      <Badge variant="outline">未下载</Badge>
+                    )}
+                  </div>
+                  {!model.downloaded && !model.downloading && (
+                    <Button
+                      size="sm"
+                      variant="outline"
+                      onClick={() => handleDownload(model.model_size, selectedType)}
+                    >
+                      <Download className="mr-1 h-4 w-4" />
+                      下载
+                    </Button>
+                  )}
+                </div>
+              ))}
+            </div>
+          </CardContent>
+        </Card>
+      )}
     </div>
   )
 }
-export default Transcriber