feat(面板): 实现浮动面板拖拽功能并优化样式

添加面板拖拽功能，允许用户通过标题栏拖动面板。重构面板样式，移除固定位置属性，改为居中显示并支持动态调整。同时添加语言面板状态管理，优化面板动画效果。

frontend/scripts/main.js

@@ -121,9 +121,65 @@ const fullscreenState = {
 const panelState = {
     configPanel: false,
     captionPanel: false,
+    languagePanel: false,
     logPanel: false
 };
 
+let panelDragState = {
+    isDragging: false,
+    currentPanel: null,
+    offsetX: 0,
+    offsetY: 0,
+    originalHeight: null
+};
+
+function initPanelDrag() {
+    document.querySelectorAll('.floating-panel').forEach(panel => {
+        const header = panel.querySelector('.panel-header');
+        if (!header) return;
+
+        header.style.cursor = 'move';
+
+        header.addEventListener('mousedown', (e) => {
+            if (e.target.tagName === 'BUTTON') return;
+
+            panelDragState.isDragging = true;
+            panelDragState.currentPanel = panel;
+
+            const rect = panel.getBoundingClientRect();
+            panelDragState.offsetX = e.clientX - rect.left;
+            panelDragState.offsetY = e.clientY - rect.top;
+            panelDragState.originalHeight = panel.offsetHeight;
+
+            panel.style.transform = 'none';
+            panel.style.height = panelDragState.originalHeight + 'px';
+        });
+
+        document.addEventListener('mousemove', (e) => {
+            if (!panelDragState.isDragging || !panelDragState.currentPanel) return;
+
+            const x = e.clientX - panelDragState.offsetX;
+            const y = e.clientY - panelDragState.offsetY;
+
+            const maxX = window.innerWidth - panelDragState.currentPanel.offsetWidth;
+            const maxY = window.innerHeight - panelDragState.currentPanel.offsetHeight;
+
+            panelDragState.currentPanel.style.left = Math.max(0, Math.min(x, maxX)) + 'px';
+            panelDragState.currentPanel.style.top = Math.max(0, Math.min(y, maxY)) + 'px';
+        });
+
+        document.addEventListener('mouseup', () => {
+            if (panelDragState.isDragging) {
+                panelDragState.isDragging = false;
+                if (panelDragState.currentPanel) {
+                    panelDragState.currentPanel.style.height = '';
+                }
+                panelDragState.currentPanel = null;
+            }
+        });
+    });
+}
+
 const logger = {
     log(level, message, data = null) {
         const timestamp = new Date().toLocaleTimeString('zh-CN', { hour12: false });
@@ -1248,6 +1304,7 @@ function init() {
     bindEvents();
     updateUIState();
     initScaling();
+    initPanelDrag();
     watchCaptionContainer();
 }