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.

app/(resources)/resources.css

@@ -220,6 +220,12 @@
   height: 100%;
 }
 
+.resources-root .resources-card-icon img {
+  width: 100%;
+  height: 100%;
+  object-fit: contain;
+}
+
 .resources-root .resources-card-has-icon .resources-card-num {
   padding-right: 60px;
 }