build(admin): track the SPA build output so git deploys carry it

assets/admin/build was gitignored, so servers deployed by git pull kept
running a stale admin bundle — the icon picker integration in the tabbar
and floating-button settings pages never reached them. Track the build
directory (rebuild with: cd assets/admin && npm run build) and commit the
current bundle containing the universal icon picker.

assets/admin/build/UsersBadge.css

@@ -0,0 +1 @@
+.medal-cat-block[data-v-fe872f5e]{margin-bottom:16px}.medal-item-row[data-v-fe872f5e]{padding:12px;border:1px solid var(--n-border-color, #efeff5);border-radius:8px;margin-bottom:8px}