Adding progress feedback to the install script

If you look at the previous demos, running bash install.sh did not feel very interactive…

There was no loading spinner, so the one-time installation could feel very long from the user’s point of view, even when the script was actually still doing useful work in the background. Because of that, in this commit I added two spinner-related modes to the install script.

The first one is the default experience: a regular spinner for long-running steps, so the installation no longer feels silent while packages are being installed, Docker is being configured, or DNS checks are running.

The second one is a --verbose mode. This is for cases where I want the real output to stay visible instead of being hidden behind the spinner. So the default mode feels cleaner for normal users, while --verbose is more useful when I need to inspect what is actually happening step by step.

It is a small step, but I think it has a big impact on the user experience. The installation flow is still doing the same work underneath, but now it feels much more alive and reassuring instead of looking like it is stuck.