refactor: migrate test runner from vitest to bun:test

- Replace vitest with bun:test across all 8 packages (47 test files)
- vi.spyOn → spyOn, vi.restoreAllMocks() → mock.restore() (3 files)
- toHaveBeenCalledOnce → toHaveBeenCalledTimes(1) (bun:test compat)
- Delete all vitest.config.ts files
- Remove vitest from devDependencies
- Add preload.ts for process.exit mock (cli-workflow)
- Fix import ordering (biome check --write)

All tests pass. Closes #601

packages/workflow-util/__tests__/frontmatter-markdown.test.ts

@@ -1,4 +1,4 @@
-import { describe, expect, it } from "vitest";
+import { describe, expect, it } from "bun:test";
 import type { AgentFrontmatter } from "../src/index.js";
 import { parseFrontmatterMarkdown, validateFrontmatter } from "../src/index.js";
 

packages/workflow-util/package.json

@@ -16,8 +16,8 @@
   },
   "scripts": {
     "prepublishOnly": "echo 'Use bun run release from repo root' && exit 1",
-    "test": "vitest run",
-    "test:ci": "vitest run"
+    "test": "bun test __tests__/ src/__tests__/",
+    "test:ci": "bun test __tests__/ src/__tests__/"
   },
   "dependencies": {},
   "devDependencies": {

packages/workflow-util/src/__tests__/ulid-timestamp.test.ts

@@ -1,4 +1,4 @@
-import { describe, expect, it } from "vitest";
+import { describe, expect, it } from "bun:test";
 import { extractUlidTimestamp, generateUlid } from "../ulid.js";
 
 describe("extractUlidTimestamp", () => {

packages/workflow-util/vitest.config.ts

@@ -1,8 +0,0 @@
-import { defineConfig } from "vitest/config";
-
-export default defineConfig({
-  test: {
-    include: ["src/__tests__/**/*.test.ts"],
-    passWithNoTests: true,
-  },
-});