test: 添加 Utils 纯函数单元测试 (测试计划 02)

覆盖 xml, hash, stringUtils, semver, uuid, format, frontmatterParser,
file, glob, diff 共 10 个模块的纯函数测试。
json.ts 因模块加载链路过重暂跳过。
共 190 个测试用例（含已有 array/set）全部通过。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/utils/__tests__/uuid.test.ts

@@ -0,0 +1,34 @@
+import { describe, expect, test } from "bun:test";
+import { validateUuid } from "../uuid";
+
+describe("validateUuid", () => {
+  test("validates correct UUID", () => {
+    const result = validateUuid("550e8400-e29b-41d4-a716-446655440000");
+    expect(result).toBe("550e8400-e29b-41d4-a716-446655440000");
+  });
+
+  test("validates uppercase UUID", () => {
+    const result = validateUuid("550E8400-E29B-41D4-A716-446655440000");
+    expect(result).not.toBeNull();
+  });
+
+  test("returns null for non-string", () => {
+    expect(validateUuid(123)).toBeNull();
+    expect(validateUuid(null)).toBeNull();
+    expect(validateUuid(undefined)).toBeNull();
+  });
+
+  test("returns null for invalid UUID format", () => {
+    expect(validateUuid("not-a-uuid")).toBeNull();
+    expect(validateUuid("550e8400-e29b-41d4-a716")).toBeNull();
+    expect(validateUuid("550e8400e29b41d4a716446655440000")).toBeNull();
+  });
+
+  test("returns null for empty string", () => {
+    expect(validateUuid("")).toBeNull();
+  });
+
+  test("returns null for UUID with invalid chars", () => {
+    expect(validateUuid("550e8400-e29b-41d4-a716-44665544000g")).toBeNull();
+  });
+});