feat: 沙盒模型合规优化 — 移除境外模型引用，新增 GET /sandbox/models 接口

- MODEL_CATALOG 仅保留国内已备案模型（DeepSeek/SenseNova）
- chat()/chatStream() modelMap 仅路由到国内 provider
- provider 命名明确化："OpenAI 兼容接口" → "硅基流动 / DeepSeek"
- 新增 getSandboxModels() 动态返回可用模型列表
- sandbox 控制器拆分 auth 级别，GET /sandbox/models 无需认证
- 新增 getAvailableModels() 供前端调用

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/src/modules/sandbox/sandbox.service.ts

@@ -3,6 +3,13 @@ import { PrismaService } from '../../prisma/prisma.service';
 import { AIGatewayService, ChatOptions } from '../ai/ai-gateway.service';
 import { randomUUID, createHmac } from 'crypto';
 
+export interface SandboxModelInfo {
+  id: string;
+  label: string;
+  provider: string;
+  desc: string;
+}
+
 interface StreamResult {
   type: 'text' | 'done' | 'error';
   content?: string;
@@ -288,6 +295,16 @@ export class SandboxService {
     };
   }
 
+  /** 返回沙箱中可用的模型列表 */
+  getAvailableModels(): SandboxModelInfo[] {
+    return this.aiGateway.getSandboxModels().map(m => ({
+      id: m.id,
+      label: m.label,
+      provider: m.provider,
+      desc: m.desc,
+    }));
+  }
+
   async generateShareToken(userId: number, sessionId: number) {
     const session = await this.prisma.sandboxSession.findFirst({
       where: { id: sessionId, userId },