feat: 扫描整理并行化、WebSocket 实时进度与统计看板

- 移动阶段并行处理文件，按原子计数上报累计进度
- 扫描遍历阶段实时上报已发现文件数，界面不再卡在 0/0
- 新增 /api/scan/ws WebSocket 实时推送扫描状态；前端断线指数退避自动重连，并以低频轮询兜底
- 新增统计看板与媒体库筛选/排序，目录选择器路径不存在时回退到最近可用父目录
- 存放目录支持自定义并持久化，默认输出到 KMP已整理

frontend/src/views/MediaList.vue

@@ -32,7 +32,7 @@
         </div>
 
         <el-table :data="list" v-loading="loading" border stripe @sort-change="handleSortChange">
-            <el-table-column prop="fileName" label="文件名" min-width="220" show-overflow-tooltip>
+            <el-table-column prop="fileName" label="文件名" min-width="100" show-overflow-tooltip>
                 <template slot-scope="scope">
                     <span class="file-name" :title="scope.row.filePath">{{ scope.row.fileName }}</span>
                 </template>
@@ -48,7 +48,7 @@
                     <span v-else>{{ scope.row.orientation }}</span>
                 </template>
             </el-table-column>
-            <el-table-column prop="resolution" label="分辨率" width="110" align="center" sortable="custom">
+            <el-table-column prop="resolution" label="分辨率" width="120" align="center" sortable="custom">
                 <template slot-scope="scope">
                     <span class="muted" v-if="!scope.row.resolution">-</span>
                     <span v-else>{{ scope.row.resolution }}</span>
@@ -60,19 +60,19 @@
                     <span v-else class="muted">-</span>
                 </template>
             </el-table-column>
-            <el-table-column prop="codec" label="编码" width="90" align="center">
+            <el-table-column prop="codec" label="编码" width="120" align="center">
                 <template slot-scope="scope">
                     <span class="muted" v-if="!scope.row.codec">-</span>
                     <span v-else>{{ scope.row.codec }}</span>
                 </template>
             </el-table-column>
-            <el-table-column prop="format" label="格式" width="80" align="center">
+            <el-table-column prop="format" label="格式" width="120" align="center">
                 <template slot-scope="scope">
                     <span class="muted" v-if="!scope.row.format">-</span>
                     <span v-else>{{ scope.row.format }}</span>
                 </template>
             </el-table-column>
-            <el-table-column prop="duration" label="时长" width="90" align="center" sortable="custom">
+            <el-table-column prop="duration" label="时长" width="120" align="center" sortable="custom">
                 <template slot-scope="scope">
                     <span class="muted" v-if="!scope.row.durationText">-</span>
                     <span v-else>{{ scope.row.durationText }}</span>
@@ -87,7 +87,7 @@
                     <span v-else>{{ scope.row.destDir }}</span>
                 </template>
             </el-table-column>
-            <el-table-column prop="createdAt" label="入库时间" width="150" align="center" sortable="custom">
+            <el-table-column prop="createdAt" label="入库时间" width="200" align="center" sortable="custom">
                 <template slot-scope="scope">
                     <span class="muted" v-if="!scope.row.createdAt">-</span>
                     <span v-else>{{ formatTime(scope.row.createdAt) }}</span>
@@ -134,7 +134,7 @@ export default {
             formatOptions: [],
             query: {
                 page: 1,
-                pageSize: 10,
+                pageSize: 20,
                 mediaType: '',
                 orientation: '',
                 resolution: '',