feat(前端界面): 精简字体管理代码，优化打开图标

assets/webui/index.html

@@ -13,7 +13,7 @@
 			<input id="fontInput" class="file-input" type="file" accept=".ttf,.otf,.ttc,font/*" multiple>
 			<input id="fontDirectoryInput" class="file-input" type="file" webkitdirectory multiple>
 			<div class="tool-group">
-				<button id="ofdButton" class="icon-button" type="button" title="打开" aria-label="打开">&#128449;</button>
+				<button id="ofdButton" class="icon-button" type="button" title="打开" aria-label="打开"><span class="open-icon" aria-hidden="true"></span></button>
 				<button id="togglePagesButton" class="icon-button" type="button" title="页面栏" aria-label="页面栏" aria-pressed="true">&#9776;</button>
 				<button id="toggleMetaButton" class="icon-button" type="button" title="信息栏" aria-label="信息栏" aria-pressed="true">&#9432;</button>
 			</div>