Prompt user to make Brave the default

Since we are detecting the distro that the user is using, we could either set Brave as the default (after prompting the user), or at least print instructions on how to do that specific to their distro.

e.g.
```
Your current default browser is: google-chrome
Would you like to make Brave the default? [Y/n]
```

https://feeding.cloud.geek.nz/posts/set-default-web-browser-debian-ubuntu/ has many of the ways that the default browser can be set.

Start by reading install.sh, especially its distro-detection and user-interaction entry points. Determine whether the project should prompt to make Brave the default or print distro-specific instructions, then verify the chosen behavior across the supported distributions and confirm that the current default browser is reported correctly.

Written by the indexing model from the issue text.