why-nix page improvements

[Sigmanificient]

As discussed with @djacu on the call, we established a list of a changes that i could directly integrate to the why-page page, which includes:

• recenter the question mark on the hero svg
• remove the section backgrounds that add too much noise to the page: style(why-nix): remove section backgrounds #2065
• increase the padding to give more breathing room (especially blue-slope sections)
• remove the card borders & move the icon
• improve text-alignment of the tech table
• rework the "my codebase" tricard (removing slopes, reducing icons size, better icon for "dev")
• minimal path fixup on the global
• change icon for for the CTA button, to clarify the action (phone -> mail): style(why-nix): clarify mail CTA #2066