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__/hash.test.ts

@@ -0,0 +1,57 @@
+import { describe, expect, test } from "bun:test";
+import { djb2Hash, hashContent, hashPair } from "../hash";
+
+describe("djb2Hash", () => {
+  test("returns a number", () => {
+    expect(typeof djb2Hash("hello")).toBe("number");
+  });
+
+  test("returns 0 for empty string", () => {
+    expect(djb2Hash("")).toBe(0);
+  });
+
+  test("is deterministic", () => {
+    expect(djb2Hash("test")).toBe(djb2Hash("test"));
+  });
+
+  test("different strings produce different hashes", () => {
+    expect(djb2Hash("abc")).not.toBe(djb2Hash("def"));
+  });
+
+  test("returns 32-bit integer", () => {
+    const hash = djb2Hash("some long string to hash");
+    expect(hash).toBe(hash | 0); // bitwise OR with 0 preserves 32-bit int
+  });
+});
+
+describe("hashContent", () => {
+  test("returns a string", () => {
+    expect(typeof hashContent("hello")).toBe("string");
+  });
+
+  test("is deterministic", () => {
+    expect(hashContent("test")).toBe(hashContent("test"));
+  });
+
+  test("different strings produce different hashes", () => {
+    expect(hashContent("abc")).not.toBe(hashContent("def"));
+  });
+});
+
+describe("hashPair", () => {
+  test("returns a string", () => {
+    expect(typeof hashPair("a", "b")).toBe("string");
+  });
+
+  test("is deterministic", () => {
+    expect(hashPair("a", "b")).toBe(hashPair("a", "b"));
+  });
+
+  test("order matters", () => {
+    expect(hashPair("a", "b")).not.toBe(hashPair("b", "a"));
+  });
+
+  test("disambiguates different splits", () => {
+    expect(hashPair("ts", "code")).not.toBe(hashPair("tsc", "ode"));
+  });
+});