test: add cross-platform launch test for electron app

[icebear0828]

This PR resolves #121 by adding an end-to-end integration test to ensure the Electron shell builds, packages, and successfully opens its main window without crashing upon launch.

Key changes:

• Adds @playwright/test, playwright, and vitest as devDependencies in packages/electron/package.json.
• Adds "test": "vitest run" script to packages/electron/package.json to enable automated local execution.
• Introduces packages/electron/__tests__/launch.test.ts to coordinate full workflow testing:
  • Compiles the frontend and backend using npm run build.
  • Packages the app logic into OS-specific unpacked directories (linux-unpacked, win-unpacked, mac) using npx electron-builder --dir.
  • Dynamically isolates the generated binary depending on OS conventions.
  • Generates a local configuration context bypassing DISABLE_NATIVE_TRANSPORT issues via a mocked local.yaml.
  • Injects a test-user-data directory parameter, boots the Playwright runtime, and asserts the successful opening of the "Codex Proxy Developer Dashboard" window.

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PR created automatically by Jules for task 17437062806426425755 started by @icebear0828

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