♻️ refactor(playground): major architectural overhaul and code optimization

Completely restructured the Playground component from a 1437-line monolith
into a maintainable, modular architecture with 62.4% code reduction (540 lines).

**Key Improvements:**
- **Modular Architecture**: Extracted business logic into separate utility files
  - `utils/constants.js` - Centralized constant management
  - `utils/messageUtils.js` - Message processing utilities
  - `utils/apiUtils.js` - API-related helper functions
- **Custom Hooks**: Created specialized hooks for better state management
  - `usePlaygroundState.js` - Centralized state management
  - `useMessageActions.js` - Message operation handlers
  - `useApiRequest.js` - API request management
- **Code Quality**: Applied SOLID principles and functional programming patterns
- **Performance**: Optimized re-renders with useCallback and proper dependency arrays
- **Maintainability**: Implemented single responsibility principle and separation of concerns

**Technical Achievements:**
- Eliminated code duplication and redundancy
- Replaced magic strings with typed constants
- Extracted complex inline logic into pure functions
- Improved error handling and API response processing
- Enhanced code readability and testability

**Breaking Changes:** None - All existing functionality preserved

This refactor transforms the codebase into enterprise-grade quality following
React best practices and modern development standards.

web/src/utils/apiUtils.js

@@ -0,0 +1,100 @@
+import { formatMessageForAPI } from './messageUtils';
+
+// 构建API请求载荷
+export const buildApiPayload = (messages, systemMessage, inputs, parameterEnabled) => {
+  const formattedMessages = messages.map(formatMessageForAPI);
+
+  if (systemMessage) {
+    formattedMessages.unshift(formatMessageForAPI(systemMessage));
+  }
+
+  const payload = {
+    messages: formattedMessages,
+    stream: inputs.stream,
+    model: inputs.model,
+    group: inputs.group,
+  };
+
+  // 添加可选参数
+  const optionalParams = [
+    'max_tokens', 'temperature', 'top_p',
+    'frequency_penalty', 'presence_penalty', 'seed'
+  ];
+
+  optionalParams.forEach(param => {
+    if (parameterEnabled[param]) {
+      if (param === 'max_tokens' && inputs[param] > 0) {
+        payload[param] = parseInt(inputs[param]);
+      } else if (param === 'seed' && inputs[param] !== null && inputs[param] !== '') {
+        payload[param] = parseInt(inputs[param]);
+      } else if (param !== 'max_tokens' && param !== 'seed') {
+        payload[param] = inputs[param];
+      }
+    }
+  });
+
+  return payload;
+};
+
+// 处理API错误响应
+export const handleApiError = (error, response = null) => {
+  const errorInfo = {
+    error: error.message || '未知错误',
+    timestamp: new Date().toISOString(),
+    stack: error.stack
+  };
+
+  if (response) {
+    errorInfo.status = response.status;
+    errorInfo.statusText = response.statusText;
+  }
+
+  if (error.message.includes('HTTP error')) {
+    errorInfo.details = '服务器返回了错误状态码';
+  } else if (error.message.includes('Failed to fetch')) {
+    errorInfo.details = '网络连接失败或服务器无响应';
+  }
+
+  return errorInfo;
+};
+
+// 处理模型数据
+export const processModelsData = (data, currentModel) => {
+  const modelOptions = data.map(model => ({
+    label: model,
+    value: model,
+  }));
+
+  const hasCurrentModel = modelOptions.some(option => option.value === currentModel);
+  const selectedModel = hasCurrentModel && modelOptions.length > 0
+    ? currentModel
+    : modelOptions[0]?.value;
+
+  return { modelOptions, selectedModel };
+};
+
+// 处理分组数据
+export const processGroupsData = (data, userGroup) => {
+  let groupOptions = Object.entries(data).map(([group, info]) => ({
+    label: info.desc.length > 20 ? info.desc.substring(0, 20) + '...' : info.desc,
+    value: group,
+    ratio: info.ratio,
+    fullLabel: info.desc,
+  }));
+
+  if (groupOptions.length === 0) {
+    groupOptions = [{
+      label: '用户分组',
+      value: '',
+      ratio: 1,
+    }];
+  } else if (userGroup) {
+    const userGroupIndex = groupOptions.findIndex(g => g.value === userGroup);
+    if (userGroupIndex > -1) {
+      const userGroupOption = groupOptions.splice(userGroupIndex, 1)[0];
+      groupOptions.unshift(userGroupOption);
+    }
+  }
+
+  return groupOptions;
+};