feat: 初始化 Nest 服务骨架与多平台 Chat SSE 网关

- 新增 NestJS + Fastify 入口、配置模块与 Swagger 集成
- 划分 client-app / admin-app 与 shared-domain ai-gateway
- 实现统一 SSE Chat 接口，支持千问、DeepSeek、火山引擎非流式上游与网关分片输出
- 补充项目方案与 JWT 最小实现文档

Made-with: Cursor

src/apps/shared-domain/ai-gateway/providers/volc.provider.ts

@@ -0,0 +1,82 @@
+import { Injectable, InternalServerErrorException } from '@nestjs/common';
+import { request } from 'undici';
+import { ProviderStreamResult, StreamChatRequest } from '../types/chat.types';
+import { AiProvider } from './provider.interface';
+
+@Injectable()
+export class VolcProvider implements AiProvider {
+  readonly code = 'volc';
+
+  supports(model?: string): boolean {
+    if (!model) return true;
+    return (
+      model.toLowerCase().includes('volc') ||
+      model.toLowerCase().includes('ark')
+    );
+  }
+
+  async streamChat(req: StreamChatRequest): Promise<ProviderStreamResult> {
+    const apiKey = process.env.VOLC_API_KEY;
+    const baseUrl =
+      process.env.VOLC_BASE_URL || 'https://ark.cn-beijing.volces.com/api/v3';
+
+    if (!apiKey) {
+      throw new InternalServerErrorException('VOLC_API_KEY 未配置');
+    }
+
+    const model = req.model || 'ep-default';
+    const upstreamBody = {
+      model,
+      stream: false,
+      messages: (req.messages || []).map((m) => ({
+        role: m.role,
+        content: m.content,
+      })),
+    };
+
+    const { statusCode, body } = await request(`${baseUrl}/chat/completions`, {
+      method: 'POST',
+      body: JSON.stringify(upstreamBody),
+      headers: {
+        'Content-Type': 'application/json',
+        Authorization: `Bearer ${apiKey}`,
+      },
+    });
+
+    if (statusCode < 200 || statusCode >= 300) {
+      const text = await body.text();
+      throw new InternalServerErrorException(
+        `火山引擎调用失败: ${statusCode} - ${text}`,
+      );
+    }
+
+    const json = (await body.json()) as any;
+    const content: string =
+      json.choices?.[0]?.message?.content ??
+      '[Volc] 未返回内容，请检查请求参数或模型配置。';
+
+    const promptTokens: number = json.usage?.prompt_tokens ?? 0;
+    const completionTokens: number = json.usage?.completion_tokens ?? 0;
+    const totalTokens: number =
+      json.usage?.total_tokens ?? Math.max(1, promptTokens + completionTokens);
+
+    const chunks = this.splitText(content, 24).map((c) => ({ content: c }));
+
+    return {
+      requestId: json.id || `volc_${Date.now()}`,
+      providerCode: this.code,
+      model,
+      chunks,
+      usage: { promptTokens, completionTokens, totalTokens },
+    };
+  }
+
+  private splitText(text: string, size: number) {
+    const result: string[] = [];
+    for (let i = 0; i < text.length; i += size) {
+      result.push(text.slice(i, i + size));
+    }
+    return result;
+  }
+}
+