Astro-nomical Improvements

[matmanna]

This PR keeps the look and feel (css) of Slacker News identical while switching the site to use Astro (a modern web framework "for content-driven websites")

Full list of improvements:

• Migrated to Astro
  • Features like theme preference adherance, @/# mentions, and RSS feeds have been retained.
  • Link/slug format is the same
• JS features are automatically hidden when JS is disabled
• Adds prettier & other things to make DX/codebase maintenance bettter

Cool things we can do now:

• More advanced react-based integrations (e.g. #ship, #ysws widgets)
• CMS (Visual Article Editing + Publishing)
• Better segregation of public and private articles as well as more seamless protection of private articles behind HCA
• Private, HCA-gated article comments (maybe synced with replies to threads in #slacker-news on Slack for easier moderation?)