feat: 新增永久删除文件接口和前端删除按钮

后端新增 POST api/files/delete 接口，同时删除物理文件、缩略图和数据库记录。
前端在 FileCard 和 FileListItem 中增加 hover 可见的删除按钮，点击后弹出确认提示。

FileShare-Web-VUE/src/components/ClientPage.vue

@@ -272,6 +272,24 @@ function exitSearch() {
   searchTotalPages.value = 0
 }
 
+async function deleteFile(file: FileRecordDto) {
+  if (!window.confirm(`确定要永久删除 "${file.fileName}" 吗？\n\n删除后无法恢复！`)) {
+    return
+  }
+  try {
+    await api.deleteFile(file.id)
+    await browseDirectory()
+    if (isSearching.value) {
+      await doSearch(searchPage.value)
+    }
+    if (selectedFile.value?.id === file.id) {
+      selectedFile.value = null
+    }
+  } catch (error) {
+    setError(error)
+  }
+}
+
 function updatePlaybackPosition(id: number, position: number) {
   if (selectedFile.value?.id === id) {
     selectedFile.value.playbackPosition = position
@@ -463,7 +481,7 @@ onBeforeUnmount(() => {
       <p v-else-if="searchResults.length === 0" class="empty-state">无匹配文件</p>
       <div v-else-if="viewMode === 'grid'" class="file-grid">
         <template v-for="file in searchResults" :key="file.id">
-          <FileCard :file="file" show-created-time @select="selectSearchFile" />
+          <FileCard :file="file" show-created-time @select="selectSearchFile" @delete="deleteFile" />
 <SelectedMediaPlayerHost
           v-if="selectedFile?.id === file.id"
           :ref="setMediaPlayer"
@@ -488,7 +506,7 @@ onBeforeUnmount(() => {
       </div>
       <div v-else class="file-list">
         <template v-for="file in searchResults" :key="file.id">
-          <FileListItem :file="file" show-created-time @select="selectSearchFile" />
+          <FileListItem :file="file" show-created-time @select="selectSearchFile" @delete="deleteFile" />
 <SelectedMediaPlayerHost
           v-if="selectedFile?.id === file.id"
           :ref="setMediaPlayer"
@@ -531,7 +549,7 @@ onBeforeUnmount(() => {
       </p>
       <div v-else-if="viewMode === 'grid'" class="file-grid">
         <template v-for="file in recentFiles" :key="file.id">
-          <FileCard :file="file" :selected="selectedFile?.id === file.id" @select="selectFile" />
+          <FileCard :file="file" :selected="selectedFile?.id === file.id" @select="selectFile" @delete="deleteFile" />
 <SelectedMediaPlayerHost
           v-if="selectedFile?.id === file.id"
           :ref="setMediaPlayer"
@@ -561,6 +579,7 @@ onBeforeUnmount(() => {
             :selected="selectedFile?.id === file.id"
             :show-last-played="activeTab === 'recent-played'"
             @select="selectFile"
+            @delete="deleteFile"
           />
 <SelectedMediaPlayerHost
           v-if="selectedFile?.id === file.id"
@@ -630,6 +649,7 @@ onBeforeUnmount(() => {
                 :selected="selectedFile?.id === file.id"
                 show-created-time
                 @select="selectFile"
+                @delete="deleteFile"
               />
 <SelectedMediaPlayerHost
           v-if="selectedFile?.id === file.id"
@@ -661,6 +681,7 @@ onBeforeUnmount(() => {
                 :selected="selectedFile?.id === file.id"
                 show-created-time
                 @select="selectFile"
+                @delete="deleteFile"
               />
 <SelectedMediaPlayerHost
           v-if="selectedFile?.id === file.id"