Remove/Address TODOs in onboarding

[TimoPtr]

Summary

This PR removes TODOs that we don't need anymore and address some of them when it makes sense.

Checklist

• New or updated tests have been added to cover the changes following the testing guidelines.
• The code follows the project's code style and best_practices.
• The changes have been thoroughly tested, and edge cases have been considered.
• Changes are backward compatible whenever feasible. Any breaking changes are documented in the changelog for users and/or in the code for developers depending on the relevance.

Any other notes

No TODO should be left from the onboarding code base the last one is going to be address in #6115

The split of the tests are in a dedicated commit that can be ignored.

[TimoPtr]

I tried it (I have a stash with the changes). I've used a value class in the AuthRepository to enforce a strong type but then this types is not properly use by the navigation library and it needs a custom NavType mapping which I don't like.

I hope this is going to work in nav3 let see, for now I'm going to keep it like this.

[TimoPtr]

All TODOs regarding the color and sytle have been removed since the design team won't have time for us and for now it looks ok. We are going to need a more general change over the app later at least for the typographie.

[TimoPtr]

Last TODOs to address are to verify the URL for the documentation and it is going to be addressed in another PR.

[jpelgrom]

Taking "No TODO should be left from the onboarding code base" very seriously:

Missed:

• android/onboarding/src/main/kotlin/io/homeassistant/companion/android/compose/composable/HAWebView.kt

  Line 56 in 6229df0

  // TODO do this in :app

• android/onboarding/src/main/kotlin/io/homeassistant/companion/android/launcher/LauncherActivity.kt

  Line 120 in 6229df0

  // TODO fail when not in FULL variant (maybe make a dedicated screen explaining that

• android/onboarding/src/main/kotlin/io/homeassistant/companion/android/onboarding/wearmtls/WearMTLSScreen.kt

  Line 272 in 6229df0

  // TODO probably wrong style and color/token

What about:

• android/onboarding/src/main/kotlin/io/homeassistant/companion/android/frontend/navigation/FrontendNavigation.kt

  Line 56 in 6229df0

  // TODO replace with strong types when WebViewActivity is available to onboarding module

  ?

• android/onboarding/src/main/kotlin/io/homeassistant/companion/android/util/TLSWebViewClient.kt

  Line 23 in 6229df0

  // TODO remove it because it's a duplicate of the one in :app

  ?

• android/onboarding/src/main/kotlin/io/homeassistant/companion/android/launcher/LauncherViewModel.kt

  Line 169 in 6229df0

  // TODO Make a page that simply show the message R.string.error_connection_failed_no_network

  ?