feat(frontend): 统一界面图标体系

frontend/src/features/workspace/FileTreeNode.vue

@@ -1,5 +1,7 @@
 <script setup lang="ts">
 import type { FileNode } from '@/contracts'
+import { Document, Folder, FolderOpened } from '@element-plus/icons-vue'
+import AppIcon from '@/components/common/AppIcon.vue'
 
 defineProps<{ node: FileNode; activePath: string | null }>()
 const emit = defineEmits<{
@@ -12,7 +14,7 @@ const emit = defineEmits<{
   <div>
     <div class="tree-node" :class="{ active: node.path === activePath }"
       @click="emit('open', node)" @contextmenu="emit('contextMenu', $event, node)">
-      <span>{{ node.type === 'folder' ? (node.is_open ? '📂' : '📁') : '📄' }}</span>
+      <AppIcon :icon="node.type === 'folder' ? (node.is_open ? FolderOpened : Folder) : Document" :size="16" />
       <span class="name">{{ node.name }}</span>
       <span v-if="node.is_dirty">●</span>
     </div>

frontend/src/features/workspace/FileTreePanel.vue

@@ -6,6 +6,8 @@ import * as workspaceService from '@/services/workspaceService'
 import { useEditorStore } from '@/stores/editor'
 import { useWorkspaceStore } from '@/stores/workspace'
 import FileTreeNode from './FileTreeNode.vue'
+import { DocumentAdd, FolderAdd } from '@element-plus/icons-vue'
+import AppIcon from '@/components/common/AppIcon.vue'
 
 const workspaceStore = useWorkspaceStore()
 const editorStore = useEditorStore()
@@ -90,8 +92,8 @@ async function deleteTarget() {
 <template>
   <section class="file-tree-panel" @click="closeContextMenu">
     <div class="toolbar">
-      <button type="button" title="新建笔记" @click.stop="beginCreate('file')">＋📄</button>
-      <button type="button" title="新建文件夹" @click.stop="beginCreate('folder')">＋📁</button>
+      <button type="button" title="新建笔记" aria-label="新建笔记" @click.stop="beginCreate('file')"><AppIcon :icon="DocumentAdd" /></button>
+      <button type="button" title="新建文件夹" aria-label="新建文件夹" @click.stop="beginCreate('folder')"><AppIcon :icon="FolderAdd" /></button>
     </div>
     <form v-if="newItemType" class="new-item" @submit.prevent="createItem">
       <input v-model="newItemName" :placeholder="newItemType === 'file' ? '笔记名称' : '文件夹名称'" autofocus />

frontend/src/features/workspace/WorkspaceView.vue

@@ -4,6 +4,8 @@ import { useWorkspaceStore } from '@/stores/workspace'
 import { useEditorStore } from '@/stores/editor'
 import EditorHeader from '@/features/editor/EditorHeader.vue'
 import EditorPane from '@/features/editor/EditorPane.vue'
+import { EditPen } from '@element-plus/icons-vue'
+import AppIcon from '@/components/common/AppIcon.vue'
 
 const workspaceStore = useWorkspaceStore()
 const editorStore = useEditorStore()
@@ -28,7 +30,7 @@ onMounted(() => {
     </template>
     <div v-else class="empty-workspace">
       <div class="empty-content">
-        <div class="empty-icon">📝</div>
+        <AppIcon class="empty-icon" :icon="EditPen" :size="48" />
         <h2>开始写作</h2>
         <p>从左侧文件树选择笔记，或创建新的笔记</p>
       </div>