refactor: 设置面板改为右侧抽屉，修复布局跳动问题

- ConfigPanel 重写为 Drawer：右侧 320px 滑入面板 + 半透明遮罩
- 设置按钮始终可见，不依赖连接状态
- 抽屉不推挤主布局，点击遮罩或✕关闭
- 设置项分组显示，带功能描述文案

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/App.css

@@ -140,7 +140,7 @@ body {
 /* ---- 左侧视频面板 ---- */
 
 .video-panel {
-  width: 340px;
+  width: 400px;
   flex-shrink: 0;
   display: flex;
   flex-direction: column;
@@ -392,44 +392,107 @@ body {
   border: 1px solid rgba(245, 158, 11, 0.2);
 }
 
-/* ---- Config Panel ---- */
+/* ---- Drawer (Config Panel) ---- */
 
-.config-panel {
+.drawer-overlay {
+  position: fixed;
+  inset: 0;
+  z-index: 100;
+  background: rgba(0, 0, 0, 0.4);
+  backdrop-filter: blur(2px);
+  animation: fadeIn 0.2s ease;
+}
+
+.drawer {
+  position: absolute;
+  top: 0;
+  right: 0;
+  bottom: 0;
+  width: 320px;
   background: var(--color-surface);
-  border-bottom: 1px solid var(--color-border);
-  padding: 16px 24px;
+  border-left: 1px solid var(--color-border);
+  display: flex;
+  flex-direction: column;
+  animation: slideInRight 0.25s ease;
+  box-shadow: -8px 0 24px rgba(0, 0, 0, 0.3);
+}
+
+.drawer__header {
   display: flex;
   align-items: center;
-  gap: 24px;
+  justify-content: space-between;
+  padding: 14px 16px;
+  border-bottom: 1px solid var(--color-border);
   flex-shrink: 0;
 }
 
-.config-panel__header {
-  display: flex;
-  align-items: center;
-  gap: 8px;
+.drawer__title {
   font-weight: 600;
-  font-size: 0.85rem;
+  font-size: 0.9rem;
 }
 
-.config-panel__close {
+.drawer__close {
   background: none;
   border: none;
   color: var(--color-text-muted);
   cursor: pointer;
-  font-size: 0.9rem;
-  padding: 2px 6px;
+  font-size: 1rem;
+  padding: 4px 8px;
+  border-radius: var(--radius-sm);
+  transition: all 0.15s;
 }
 
-.config-panel__close:hover {
+.drawer__close:hover {
+  background: var(--color-surface-2);
   color: var(--color-text);
 }
 
+.drawer__body {
+  flex: 1;
+  overflow-y: auto;
+  padding: 16px;
+}
+
+/* ---- Config Group ---- */
+
+.config-group {
+  margin-bottom: 20px;
+}
+
+.config-group__title {
+  font-size: 0.7rem;
+  font-weight: 600;
+  text-transform: uppercase;
+  letter-spacing: 0.8px;
+  color: var(--color-text-muted);
+  margin-bottom: 12px;
+  padding-bottom: 8px;
+  border-bottom: 1px solid var(--color-border);
+}
+
 .config-row {
   display: flex;
   align-items: center;
-  gap: 8px;
+  justify-content: space-between;
+  padding: 10px 0;
   font-size: 0.82rem;
+  color: var(--color-text);
+  cursor: pointer;
+}
+
+.config-row__info {
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+}
+
+.config-row__label {
+  font-weight: 500;
+  color: var(--color-text);
+}
+
+.config-row__desc {
+  font-size: 0.72rem;
   color: var(--color-text-muted);
 }
 
@@ -439,8 +502,15 @@ body {
   color: var(--color-text);
   border: 1px solid var(--color-border);
   border-radius: var(--radius-sm);
-  padding: 4px 8px;
+  padding: 5px 10px;
   font-size: 0.8rem;
+  cursor: pointer;
+}
+
+.config-row input[type="checkbox"] {
+  width: 18px;
+  height: 18px;
+  cursor: pointer;
 }
 
 /* ---- Toast ---- */
@@ -559,6 +629,16 @@ body {
   to { opacity: 1; transform: translateX(0); }
 }
 
+@keyframes fadeIn {
+  from { opacity: 0; }
+  to { opacity: 1; }
+}
+
+@keyframes slideInRight {
+  from { transform: translateX(100%); }
+  to { transform: translateX(0); }
+}
+
 /* ---- Scrollbar ---- */
 
 ::-webkit-scrollbar {