Add more custom elements and styles for news posts

[cl8n]

mostly to help reduce dependence on html/css in post content but also this should just make it easier to write news posts and be consistent about styling. the following should have directives similar to Infobox:

• Video player for assets.ppy.sh, YouTube, and Twitch vods
• Audio player at full page width (and maybe with customizable audio group?)
• "Chat" layout for interviews

see https://osu.ppy.sh/home/news/2024-11-04-resurrection-cup-2024-results and https://osu.ppy.sh/home/news/2024-10-07-osumania-4k-world-cup-2024-concludes for some examples

the chat one probably needs some design consideration first though.

[Walavouchey]

• pdf viewer https://osu.ppy.sh/home/news/2023-06-26-osumonthly-9
• user links with card pop-ups On-hover user card display for profile links on the wiki #8932

audio players could always be full width in news posts imo. i'm pretty sure they're only fixed-width because that's how they appear at the bottom-right corner of the page (was mentioned internally)

[0x84f]

it would be great if we could add a photo album thing as well, it would work wonders for coverage of real-life events where lots of photos are taken