feat: implement customizable horizontal layout for error page

[d-loose]

This updates the error page to use the horizontal layout that is used on most other pages, and adds an error parsing method for customization.
I've also added a custom error parser for autoinstall errors:

Screencast.From.2026-03-04.13-42-57.webm

UDENG-8914

[juanruitina]

Looks pretty good, some minor UI tweaks:

• Given technical details shows what I understand is a raw error message, I'd suggest to make it monospaced. Also, please make sure font size matches bodyMedium.
• When clicking on "Import", I'd favour having a more standard behaviour: icon becomes disabled, label is replaced with orange spinning wheel.
• When error screen shows, remove green "close" button, it's redundant with the window close button, "Restart installer" should be the primary action (in green) instead.
• When import succeeds, the component that shows the content of the yaml file should have some padding between border and text, you may use the same the "Technical details" box uses.

[d-loose]

Updated:

Screencast.From.2026-03-05.14-58-20.webm

@matthew-hagemann do you remember if there was a reason to remove the padding from the confirmation page when displaying the autoinstall contents?

ubuntu-desktop-provision/apps/ubuntu_bootstrap/lib/pages/confirm/confirm_page.dart

Lines 81 to 82 in ce6beb7

	padding:
	status?.interactive == false ? null : kWizardTilePadding,

Changed in #982

[matthew-hagemann]

Updated:
Screencast.From.2026-03-05.14-58-20.webm

@matthew-hagemann do you remember if there was a reason to remove the padding from the confirmation page when displaying the autoinstall contents?

ubuntu-desktop-provision/apps/ubuntu_bootstrap/lib/pages/confirm/confirm_page.dart

Lines 81 to 82 in ce6beb7

	padding:
	status?.interactive == false ? null : kWizardTilePadding,

Changed in #982

@d-loose I see in the PR I wrote that the margins ended up being too large with the autoinstall confirmation text, but I don't remember the specifics 🤔

Looking at the screen shot from then though, the margins are different to whats in your screen recording, so not sure if something else has changed padding wise elsewhere? Maybe my workaround can be safely reverted?

Current:

My PR:

[juanruitina]

(The padding in the screenshot current looks more sensible)

[matthew-hagemann]

Looks good! I had one small question re: function signatures of the error parser, but otherwise happy with the approach 🙂

[matthew-hagemann]

Thanks! LGTM 🙂