[Code health] Reorganize component files

[gino-m]

• Most folders in app/services contain one impl file and one test. For that reason, sub-folders under services/ don't provide much value. Let's move the service files up one level?
• Similarly, the deep nesting of components in the pages/ folder seems to provide little value; we can flatten those to their relative page as well.
• Lastly, @rfontanarosa suggested all components should be under components/. To that end, we can move components/* to components/shared and folders in pages/ to components/.

@rfontanarosa Wdyt?

[gino-m]

@rfontanarosa Fyi, according to https://angular.dev/style-guide#organize-your-project-by-feature-areas:

Avoid creating subdirectories based on the type of code that lives in those directories. For example, avoid creating directories like components, directives, and services.

That said, I think "pages" is a very well-defined and discoverable definition of product features here. Also, most services provides logic needed by multiple features, so not sure how we would organize those better. I'd say let stick with the proposed structure above unless someone comes up with a better one.