fix(types): correct chooseFile return type to Promise<string>

[samliburd]

Changes

• Changed chooseFile() return type from string to Promise<string>

Reason

The Swift implementation shows this method is async (returns a Promise), but the TypeScript definitions have it down as synchronous. This causes TypeScript errors when using await with this method and IINA resolves the file as [object Promise] when not using await.

Evidence

Swift implementation shows Promise-based behavior:

func chooseFile() -> Any {
    return createPromise { resolve, reject in
        // async operation
        resolve.call(withArguments: [result.path])
    }
}

Link to swift file:

• https://github.com/iina/iina/blob/84cc736666e77fc051e5785e1215eee7bb06f87f/iina/JavascriptAPIUtils.swift#L231