Restore Electron rebuild after tests

[sachasayan]

This change ensures that the development environment is automatically restored to an Electron-compatible state after running tests. Previously, running tests would leave native modules (like better-sqlite3) built for Node, causing the Electron application to fail until a manual rebuild was performed.

Key changes:

• Added posttest hook in package.json to trigger a rebuild after tests finish.
• Updated rebuild:electron script to use electron-builder install-app-deps, which is more robust than the previous npx @electron/rebuild command in this environment.
• Maintained existing npm script structure as per repository conventions.

---

PR created automatically by Jules for task 15969555635906834424 started by @sachasayan

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.