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/AttachmentPermissions.css

@@ -0,0 +1 @@
+.aksrt-attach__summary[data-v-d6037ce3]{display:flex;align-items:center;gap:10px;padding:12px;border-radius:6px;background:#fafafa}.aksrt-attach__summary strong[data-v-d6037ce3]{display:block;font-size:13px;color:var(--aksrt-color-text)}.aksrt-attach__summary p[data-v-d6037ce3]{margin:2px 0 0;font-size:12px;color:var(--aksrt-color-muted)}