fix(rebar): pass the ③ material to C15/C16, coping bottom and column bars

The stair bars in the 철근표 and the 3D model, and the 3D bottom and column bars, were built with the default fck,
so a changed fck did not reach them. buildRebar3D now takes the material, and a material change rebuilds the scene.

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

src/view/rebar3d.ts

@@ -5,7 +5,7 @@ import { bottomPiece, MAIN, widthLayout } from '../core/rebar/coping-main';
 import { C14_INSET, c14Bars, CAP, COPING_REBAR, shearBars, shearBarsMulti, shearUHeight, copingSideBars, SIDE_HOOK_LEG, stairBars, undersideAt } from '../core/rebar/coping';
 import { columnRebar, COLUMN_P1 } from '../core/rebar/column';
 import { barsAcross, BLOCK_REBAR } from '../core/rebar/bearing-block';
-import { hookLength, NOMINAL_DIAMETER } from '../core/rebar/common';
+import { DEFAULT_MATERIAL, hookLength, Material, NOMINAL_DIAMETER } from '../core/rebar/common';
 import { stretchMatrix } from './scene';
 
 /**
@@ -34,7 +34,7 @@ const COLOR = {
 
 const mm = (v: number) => v / 1000;
 
-export function buildRebar3D(m: PierModel): RebarScene {
+export function buildRebar3D(m: PierModel, mat: Material = DEFAULT_MATERIAL): RebarScene {
   const group = new THREE.Group();
   const byName = new Map<string, THREE.Mesh[]>();
   const Ms = m.stretches.map((_, k) => stretchMatrix(m, k));
@@ -87,7 +87,7 @@ export function buildRebar3D(m: PierModel): RebarScene {
     // at each end to the C1 level. Each bar is two pieces spliced at the column centre (overlap l_s). The slope runs x_L0 from each end (T형).
     const xL0 = L / 2 - COPING_REBAR.levelWidth / 2000;
     const under = (x: number) => undersideAt(L * 1000, x * 1000, m.endBottom, m.levelBottom);
-    const lap = bottomPiece().ls / 2000;
+    const lap = bottomPiece(mat).ls / 2000;
     xs.forEach((n, j) => {
       const z = (x: number) => under(x) + 0.127;
       const left: [number, number, number][] = [
@@ -166,7 +166,7 @@ export function buildRebar3D(m: PierModel): RebarScene {
       }
     }
     // C15 (거꾸로 된 U) and C16 (L형) on the stair (코핑철근.md §7): 11 bars each across the width.
-    const stairs = stairBars(L * 1000, B * 1000, topEl);
+    const stairs = stairBars(L * 1000, B * 1000, topEl, mat);
     for (const s of stairs.c15) {
       const n = mm(s.n);
       const ld = mm(s.leg);
@@ -187,7 +187,7 @@ export function buildRebar3D(m: PierModel): RebarScene {
   }
 
   // Columns: P1 / P2 main bars on their radii, ties P3 / P5 / P4 as rings, P6 crossties across the column.
-  const col = columnRebar(COLUMN_P1);
+  const col = columnRebar(COLUMN_P1, mat);
   const zBot = col.zBot; // mm
   const ring = (name: string, k: number, sc: number, y: number, r: number, d: number) => {
     const N = 36;