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-protocol/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 src/__tests__/",
+    "test:ci": "bun test src/__tests__/"
   },
   "dependencies": {
     "@ocas/core": "^0.1.1",