fix: 添加延迟确保批量 Deep Scan 严格限制并发为 2

问题：
- re_scan_file API 是异步的，立即返回成功
- 后端可能同时启动多个扫描任务
- 导致有 4 个文件同时在 scanning 状态

临时修复：
- 在每个文件启动扫描后等待 2 秒
- 确保后端有足够时间开始处理并释放资源
- 保持前端并发控制为 2，避免过多任务同时启动

未来改进：
- 需要在后端实现真正的队列机制
- 或者检查当前 scanning 状态，动态调整启动速度

src/views/LibraryView.vue

@@ -1899,54 +1899,57 @@ async function batchDeepScan() {
   
   actionMsg.value = `Starting: ${immediateCount} immediate, ${queueTotal} queuing...`
   
-  const tasks = filesToProcess.map((f) => {
-    return limit(async () => {
-      const fileUuid = f.file_uuid
-      if (!fileUuid) {
+  async function processFile(f: any) {
+    const fileUuid = f.file_uuid
+    if (!fileUuid) {
+      failCount++
+      return
+    }
+    
+    processing++
+    const queueCount = Math.max(0, filesToProcess.length - successCount - failCount - processing)
+    
+    if (queueCount > 0) {
+      actionMsg.value = `Processing ${successCount + 1}/${filesToProcess.length} (${queueCount} queuing)...`
+    } else {
+      actionMsg.value = `Processing ${successCount + 1}/${filesToProcess.length}...`
+    }
+    
+    try {
+      const file = filesCache.value.find((x: any) => x.file_uuid === fileUuid)
+      if (!file) {
         failCount++
+        processing--
         return
       }
       
-      processing++
-      const queueCount = Math.max(0, filesToProcess.length - successCount - failCount - processing)
+      const result: any = await apiCall('re_scan_file', {
+        fileUuid: fileUuid,
+        autoPipeline: true
+      })
       
-      if (queueCount > 0) {
-        actionMsg.value = `Processing ${successCount + 1}/${filesToProcess.length} (${queueCount} queuing)...`
+      if (result.success) {
+        successCount++
+        if (file) {
+          file.status = 'scanning'
+          fileStatusCache.value[fileUuid] = 'scanning'
+          await syncFileStatus(fileUuid)
+        }
+        
+        // 等待 2 秒，确保后端开始处理并释放资源
+        await new Promise(resolve => setTimeout(resolve, 2000))
       } else {
-        actionMsg.value = `Processing ${successCount + 1}/${filesToProcess.length}...`
-      }
-      
-      try {
-        const file = filesCache.value.find((x: any) => x.file_uuid === fileUuid)
-        if (!file) {
-          failCount++
-          processing--
-          return
-        }
-        
-        const result: any = await apiCall('re_scan_file', {
-          fileUuid: fileUuid,
-          autoPipeline: true
-        })
-        
-        if (result.success) {
-          successCount++
-          if (file) {
-            file.status = 'scanning'
-            fileStatusCache.value[fileUuid] = 'scanning'
-            await syncFileStatus(fileUuid)
-          }
-        } else {
-          failCount++
-        }
-      } catch (e: any) {
         failCount++
-        console.error('[batchDeepScan] Failed:', f.file_name, e)
-      } finally {
-        processing--
       }
-    })
-  })
+    } catch (e: any) {
+      failCount++
+      console.error('[batchDeepScan] Failed:', f.file_name, e)
+    } finally {
+      processing--
+    }
+  }
+  
+  const tasks = filesToProcess.map((f) => limit(() => processFile(f)))
   
   await Promise.all(tasks)