feat(AI服务)：lpt-ai 独立服务初始版本

- Fastify + TypeScript，OpenAI 兼容接口对接 SiliconFlow
- POST /ai/aggregate-report：残片聚合为学习报告（支持预期对比）
- POST /ai/generate-mind-map：生成思维导图缩进大纲（与后端解析格式一致）
- Key 从环境变量读取且日志脱敏，未配置时返回 503 由调用方降级
- prompt 模板集中管理，vitest 单元测试

src/llm/prompts.test.ts

@@ -0,0 +1,46 @@
+import { describe, expect, it } from "vitest";
+import { aggregateReportPrompt, generateMindMapPrompt } from "./prompts.js";
+
+describe("aggregateReportPrompt", () => {
+  it("包含全部残片和任务名", () => {
+    const messages = aggregateReportPrompt("Java 并发", [
+      { content: "corePoolSize 是核心线程数" },
+      { content: "workQueue 满后创建新线程", createdTime: "2026-07-01" },
+    ]);
+    expect(messages).toHaveLength(2);
+    expect(messages[0].role).toBe("system");
+    expect(messages[1].content).toContain("Java 并发");
+    expect(messages[1].content).toContain("corePoolSize");
+    expect(messages[1].content).toContain("workQueue");
+    expect(messages[1].content).toContain("2026-07-01");
+  });
+
+  it("有预期时包含预期内容和对比要求", () => {
+    const messages = aggregateReportPrompt(
+      "Java 并发",
+      [{ content: "x" }],
+      "理解线程池核心参数",
+    );
+    expect(messages[1].content).toContain("理解线程池核心参数");
+    expect(messages[0].content).toContain("预期");
+  });
+
+  it("无预期时不包含预期块", () => {
+    const messages = aggregateReportPrompt("Java 并发", [{ content: "x" }]);
+    expect(messages[1].content).not.toContain("预期目标");
+  });
+});
+
+describe("generateMindMapPrompt", () => {
+  it("要求输出缩进大纲且包含全部输入", () => {
+    const messages = generateMindMapPrompt(
+      "Java 并发",
+      "并发编程学习",
+      ["报告一"],
+      ["残片一", "残片二"],
+    );
+    expect(messages[0].content).toContain("缩进");
+    expect(messages[1].content).toContain("报告一");
+    expect(messages[1].content).toContain("残片二");
+  });
+});