Implement Compose-based Error Panel , Error UI Model , and Tests for Comments

[SttApollo]

What is it?

• Feature (user facing)
• Codebase improvement (dev facing)

Description of the changes in your PR

• Created a new Compose-based ErrorPanel component.
• Ensured the new error panel is fully theme-adaptive using MaterialTheme.colorScheme and that all text is centered for visual parity with the legacy design.
• Introduced a new ErrorPanelSpec data class to flexibly describe error panel content and actions.
• Created ErrorUiModel interface to represent different failure states along with UnableToLoadCommentsUiModel specific to Comments section.
• Added a focused test suite: Unit tests for ErrorUiModel and Integration tests for the two main error states in the comment section: Resource.Error (initial load failure) and LoadState.Error (paging failure). Would add Compose testing with approval to add a new dependency.
• Manual Testing: Verified error handling by forcing errors in both CommentsViewModel (Resource.Error) and CommentsSource (LoadState.Error) to ensure proper UI rendering and error model mapping.

Before/After Screenshots/Screen Record

Before	After

Fixes the following issue(s)

• Fixes CommentSection: Add an error panel #11716

APK testing

The APK can be found by going to the "Checks" tab below the title. On the left pane, click on "CI", scroll down to "artifacts" and click "app" to download the zip file which contains the debug APK of this PR. You can find more info and a video demonstration on this wiki page.

[SttApollo]

@Stypox Apologies for the fairly large diff—thought it would make sense to add a new Compose-based ErrorPanel and have it wired up end-to-end as a first step towards migration. I’m happy to split it up or tweak anything to fit the overall architecture—just let me know!

[Stypox]

Thank you! I think this PR is the right size, and also you wrote many tests which increase the "PR line count" but do not add reviewing complexity, so there is no need to split it. And thanks for also writing test! I left a few comments to try to make the code more general so it can be used more seamlessly in other places in the app in the future (to replace other error panels in various places).

[SttApollo]

@Stypox I have incorporated your requests - removed the other files and just added one test file. Also I didn't want to add an additional dependency for compose testing but please let me know if you'd like me to!

[absurdlylongusername]

@Stypox I have incorporated your requests - removed the other files and just added one test file. Also I didn't want to add an additional dependency for compose testing but please let me know if you'd like me to!

@SttApollo Tbh I have no qualms with you adding compose testing, because we are going to be adding UI tests very soon anyway. Currently we have no UI tests whatsoever, and I don't really see a downside to having tests for new functionality.

@Stypox, thoughts?

[Stypox]

Yeah it would be cool if you added some tests! Would you be ok with opening a new PR after this one is merged, to setup the UI tests infrastructure and add tests for what you added in this PR? Otherwise you can also add UI tests in this PR, let us know what you prefer :-)

[SttApollo]

Sure, I can open a new PR after this one is merged. For the UI test infra, I was thinking we could start with Compose instrumented testing—does that align with what you had in mind? Or should we also add Robolectric-based Compose tests and/or snapshot testing early on?