Update “Why Vala?” Section to use a bullet point list

The old items in the section will be replaced with a list of of more focused reasons for using Vala, better highlighting the language’s strengths.

Here’s a general outline (should be tweaked): Here's the proposed bullet list that we should stick onto the front page (titles & subtitles):

• Clear and familiar syntax — productive from the first day
• Object-oriented when you need it — classes, interfaces, inheritance, or just functions and structs
• Automatic memory management — without a garbage collector
• Seamless C interoperability — use existing C libraries naturally
• Compiles to native binaries — no VM, no runtime environment to install
• Modern language features — type inference, null safety, generics, lambdas, async/await
• First-class GObject and GTK support — optional, but unmatched when you need it