Use the real hack.build logo and fix the showcase grid

- Replace the hand-drawn wrench with the actual hack.build mark: isolate the
  pink wrench from the brand PNG onto transparent (public/hackbuild-mark.png)
  and use it for the talk tile and the Resources card.
- Showcase grid: 7 columns so the seven projects fill one row, and draw the
  hairlines from per-tile borders instead of a grey container showing through
  gaps — no more grey empty cells on an incomplete row.
- Drop the now-unused HackBuildIcon.

components/resources/icons.tsx

@@ -123,19 +123,3 @@ export function PlayIcon(props: IconProps) {
     </svg>
   )
 }
-
-// hack.build — the brand's hot-pink open-end wrench (an open "C" head at the
-// top-right with a diagonal handle to the lower-left).
-export function HackBuildIcon(props: IconProps) {
-  return (
-    <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 48 48" fill="none" {...props}>
-      <path
-        d="M32.6 8.1 A9 9 0 1 0 39.9 15.4"
-        stroke="#ff179a"
-        strokeWidth={6.5}
-        strokeLinecap="round"
-      />
-      <path d="M25 23 L13.5 33.5" stroke="#ff179a" strokeWidth={7} strokeLinecap="round" />
-    </svg>
-  )
-}