Change code block highlighting from Prism to Arborium

[hazre]

Description

I was inspired by this tweet. https://fxtwitter.com/DiscordPreviews/status/2036671398265995336

• replace Prism-based code block highlighting with Arborium for timeline code blocks and text previews
• add Arborium theme metadata, runtime wiring, and a code block theme setting that matches the existing System Theme pattern, with system light/dark selections plus a single manual override
• extract a reusable SettingMenuSelector, remove NotificationModeSwitcher, and reuse the shared selector in notification, room, and theme settings
• wrap rendered code blocks so long lines break in both highlighted messages and text previews instead of forcing wide horizontal overflow

The cool thing about Arborium is that all the language support and themes are loaded from a CDN. So you basically ship nothing and on demand, it downloads the proper grammer for each language that shows up in the messages. fallback is just no syntax highlighting.

Sceenshots

Recording.2026-03-28.224825-00.00.00.000-00.00.17.936.mp4

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

AI disclosure:

• Partially AI assisted (clarify which code was AI assisted and briefly explain what it does).
• Fully AI generated (explain what all the generated code does in moderate detail).

The main change in this PR is replacing the old Prism-based highlighting path with Arborium for rendered message code blocks and text previews. The message renderer and text viewer now go through the Arborium-backed code highlight renderer, Arborium themes are loaded through the new theme bridge instead of the old Prism theme classes, and unsupported or failed language/theme loads still fall back safely to plain rendered code. The settings work in this PR now exposes code block theming with the same structure as the existing app theme controls: a System Theme toggle that keeps separate light and dark Arborium theme selections, plus a single Manual Theme selector that can override them when system mode is off. The reusable SettingMenuSelector extraction is supporting cleanup that lets the same dropdown pattern drive notification settings, room notification controls, and the theme pickers while removing the older one-off switcher component. The wrapping changes are the last part of that migration work: Arborium-rendered code now wraps in both timeline messages and text previews so long lines stay readable without forcing wide overflow. The tests cover Arborium theme selection and loading, selector reuse, notification option reuse, and the message/text-viewer code block regressions.

[hazre]

Okay I added a better theme selector as well. I think this is ready to go.

[7w1]

merge conflicts D:

[hazre]

Yeah my own PR is bringing me pain

[github-actions]

Deploying with    Cloudflare Workers

Status	Preview URL	Commit	Alias	Updated (UTC)
✅ Deployment successful!	https://pr-576-sable.raspy-dream-bb1d.workers.dev	3bb692f	pr-576	Mon, 30 Mar 2026 21:32:29 GMT

[7w1]

code lgtm. appears to function properly and styles are consistent