fix: handle empty editor state to clear graph and validation

[sakshammjn]

Summary

This PR fixes how the app behaves when the editor is empty.

Before this change, if all text was deleted from Monaco, the graph could still stay on screen and the validation bar could still look valid. Also, switching JSON/YAML while empty could bring back default content.

Now, when the editor is empty:

• the graph is cleared
• validation shows an error (Schema cannot be empty)
• switching format keeps the editor empty instead of resetting content

What kind of change does this PR introduce

Bug fix

Issue Number

Closes #180

Video

screen.recording.for.pr.mov

Does this PR introduce a breaking change?

No

If relevant, did you update the documentation?

No need to update the documentation

[18mukeshram]

Great fix! I was going through the issue and noticed the root cause was the early return skipping state reset.

One thought — would it also make sense to explicitly reset any cached/derived state (if present) to avoid inconsistencies in future updates?

Also, are there any edge cases around whitespace-only input or rapid toggling between formats that we should guard against?

Happy to help test or contribute further if needed.