Unit Testing Before Building the App (high priority)

[ChristophGeske]

Right now errors are only caught when the app is built and run. Adding tests that run before building the app would help catch problems earlier.

Benefits:

1. Stops the LLM from deleting working code by giving it better feedback.

2. Finds small bugs before they turn into bigger problems later.

3. Gives the LLM a clearer view of what's working and what's broken.

4. Saves time on manual testing, especially for apps with many features.

5. More useful as apps get bigger, so better to add this now than later.