feat: 实现会话配置与多轮上下文

- 新增 ConfigPanel 组件：TTS 开关、detail level、语言选择
- 新增 storage.ts：配置持久化到 localStorage
- useVisionSession：连接后自动发送 config，维护最近 10 轮对话历史
- App：齿轮按钮展开配置面板，HD 角标，TTS 播放联动 ttsEnabled

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

frontend/src/components/ConfigPanel/index.tsx

@@ -0,0 +1,55 @@
+// ============================================================
+// ConfigPanel — 会话配置面板
+// 职责：TTS 开关、detail level 切换、语言选择
+// ============================================================
+
+import type { SessionConfig } from "../../types";
+
+interface ConfigPanelProps {
+  config: SessionConfig;
+  onUpdate: (partial: Partial<SessionConfig>) => void;
+  onClose: () => void;
+}
+
+export function ConfigPanel({ config, onUpdate, onClose }: ConfigPanelProps) {
+  return (
+    <div className="config-panel">
+      <div className="config-panel__header">
+        <span>设置</span>
+        <button className="config-panel__close" onClick={onClose}>✕</button>
+      </div>
+
+      <label className="config-row">
+        <span>语音回答</span>
+        <input
+          type="checkbox"
+          checked={config.ttsEnabled}
+          onChange={(e) => onUpdate({ ttsEnabled: e.target.checked })}
+        />
+      </label>
+
+      <label className="config-row">
+        <span>图像精度</span>
+        <select
+          value={config.detailLevel}
+          onChange={(e) => onUpdate({ detailLevel: e.target.value as "low" | "high" })}
+        >
+          <option value="low">低（省流量）</option>
+          <option value="high">高（细节丰富）</option>
+        </select>
+      </label>
+
+      <label className="config-row">
+        <span>语言</span>
+        <select
+          value={config.language}
+          onChange={(e) => onUpdate({ language: e.target.value })}
+        >
+          <option value="zh-CN">中文</option>
+          <option value="en-US">English</option>
+          <option value="ja-JP">日本語</option>
+        </select>
+      </label>
+    </div>
+  );
+}