feat(view): ④ 재료표 as its own result stage, with pier selection, Excel per pier and print

The 철근재료표 moves from ③ to a new stage ④ in the header. It shows the checked piers (or the current one), one table
per pier with 강종 → 직경 → 번호 and subtotals, and a total across piers. The Excel export has one sheet per pier and a
합계 sheet. Print uses A4 landscape without the header and buttons. ③ keeps a summary line and a link to ④.
Spec §5, §6.9 and §7 record the stage (approved 2026-10-23).

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>

src/style.css

@@ -709,3 +709,16 @@ body { background: #eef1f4; font-family: 'Noto Sans KR', system-ui, sans-serif;
 .viewer-head .rebar-color { margin: 0 auto; }
 .rebar-select { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; margin: 6px 0; }
 .rebar-select .btn { min-height: 44px; }
+
+/* ④ 재료표 (승인 2026-10-23) */
+.grid.quantity { grid-template-columns: 260px minmax(0, 1fr); }
+.quantity .subtotal td { font-weight: 700; background: #f3f6fa; }
+.quantity h3 { margin: 14px 0 4px; font-size: 15px; }
+@media print {
+  @page { size: A4 landscape; margin: 10mm; }
+  body * { visibility: hidden; }
+  #view-quantity, #view-quantity * { visibility: visible; }
+  #view-quantity { position: absolute; left: 0; top: 0; width: 100%; padding: 0; }
+  #view-quantity .piers, #quantity-export, #quantity-print { display: none !important; }
+  .quantity .rebar-table { font-size: 10px; }
+}