perf: optimize katex config, implement async css loading for katex, improve scrollbar and lightbox loading logic

src/components/Widgets/GithubCard.astro

@@ -11,7 +11,7 @@ function setupGithubCards() {
         observer.unobserve(entry.target)
       }
     })
-  }, { rootMargin: '200px' })
+  }, { rootMargin: '400px' })
 
   githubCards.forEach(card => observer.observe(card))
 }