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-dashboard/package.json

@@ -6,8 +6,8 @@
   "scripts": {
     "dev": "bun server.ts",
     "build": "vite build",
-    "test": "vitest run",
-    "test:ci": "vitest run"
+    "test": "bun test src/",
+    "test:ci": "bun test src/"
   },
   "dependencies": {
     "@base-ui/react": "^1.5.0",
@@ -33,10 +33,8 @@
     "@types/react": "^19.2.14",
     "@types/react-dom": "^19.2.3",
     "@vitejs/plugin-react": "^6.0.2",
-    "@vitest/ui": "^4.1.7",
     "tailwindcss": "^4.2.4",
     "typescript": "^5.8.3",
-    "vite": "^8.0.13",
-    "vitest": "^4.1.7"
+    "vite": "^8.0.13"
   }
 }