[UI/UX] Loading / Processing Animation ...

Currently Excalibur shows a manual 'Refresh' page for long running process or failures (Reference:
https://github.com/camelot-dev/excalibur/issues/69). This is not a good UX. We need a better loading screening with an animation to let users know processing in happening or failed.

Perhaps the animation would make waiting enjoyable, if the process fails show an error and take the user back to the previous step.

Start by reviewing the current manual “Refresh” page and the behavior described in issue #69. Define the loading, processing, and failure states, including the error message and return to the previous step; done means users receive clear feedback instead of a manual refresh page.

Written by the indexing model from the issue text.