Fix external URL handler signature in main.dev.js

[hellosamyak]

Summary:
Remove accidental TypeScript annotation from JavaScript file and make URL handler synchronous for correct use in setWindowOpenHandler.

Why:
The previous function signature caused JS compile errors, and async returned a Promise where a boolean was expected.

File:
app/main.dev.js

[hellosamyak]

@lrasmus could you please take a look at this small fix PR when you get a chance?

[lrasmus]

@hellosamyak - I am curious when you got the javascript compile error? I do not recall seeing that on my end. Did the function not work when you were testing it? I just want to understand exactly the steps to reproduce the problem so that I can make a note to similarly test in the future.

[hellosamyak]

@lrasmus Hi Luke, thanks for asking.

I should clarify: I did not hit a webpack/electron build failure from this change while running yarn dev. The app still launched.
What I saw was an editor/type-check diagnostic in VS Code on [main.dev.js] at the function signature using url: string inside a .js file.
So the “compile error” wording from me was imprecise; it was a JS/TS language-service error in the Problems panel, not a runtime bundling crash.

Repro steps I used:

1. Checkout the pre-fix code where handleUrl is declared as async function handleUrl(url: string) in main.dev.js.
2. Open that file in VS Code with JavaScript validation enabled.
3. Observe the Problems panel message: “Type annotations can only be used in TypeScript files.”

Runtime note:

• In my smoke testing, the app still started.
• But I changed the function to synchronous because it is used in a boolean condition in setWindowOpenHandler; async returns a Promise there, which is not ideal for that flow.

So the fix was mainly to remove editor/type-check noise and align the handler behavior with how it is consumed.