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.

next-env.d.ts

@@ -1,6 +1,6 @@
 /// <reference types="next" />
 /// <reference types="next/image-types/global" />
-import "./.next/types/routes.d.ts";
+import "./.next/dev/types/routes.d.ts";
 
 // NOTE: This file should not be edited
 // see https://nextjs.org/docs/app/api-reference/config/typescript for more information.