Upgrade Astro (5 -> 7)

[Shiroizu]

Current: 5.18.2
Latest: 7.1.6 https://github.com/withastro/astro/blob/main/packages/astro/CHANGELOG.md

• https://astro.build/blog/astro-6/
• https://astro.build/blog/astro-7/

Benefits

• DX & Performance

• Security fixes

• Live Content Collections

• [[Wikilink]] support through Sätteri

Prerequisites

• Content Layer migration
• Tailwind 3 -> 4