Refactor frontend sections to use Tailwind CSS

Convert custom CSS styling to Tailwind utility classes across marketing
and about pages. Improve responsive layouts in feature grids, service
lists, and sliders. Consolidate section headers using the shared
SectionHeader component to maintain visual consistency.

apps/frontend/src/sections/TeamsHero.astro

@@ -36,7 +36,7 @@ const bgImageUrl = backgroundImage?.url || "";
     // Background color fallback
     !hasBackgroundImage && "bg-(--color-dark-blue)",
     // Background image styles
-    hasBackgroundImage && "bg-size-[120vw] bg-center bg-no-repeat",
+    hasBackgroundImage && "bg-cover bg-center bg-no-repeat",
     // Pull up to counteract layout's pt-20 padding (80px)
     "-mt-20",
     // Full viewport height