feat(rebar): 상면 주철근(C1–C6) 이음 무시/반영, 위치 기둥 중심/단부

- 기본 '이음 무시' (사양 결정). '반영'이면 정척(12000) 초과 철근을 l_s 겹침 2조각으로 나눔
- 위치: 기둥 중심 = 전체의 절반, 단부 = 정척 안에서 가장 끝 쪽 (짧은 조각 = 전체 + l_s − 12000, 긴 조각 = 12000)
- 철근표 조각 목록과 비고, 3D 두 조각(l_s 겹침)에 반영
- STANDARD_BAR를 common.ts로 옮겨 순환 import 방지

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

src/view/rebar3d.ts

@@ -1,7 +1,7 @@
 import * as THREE from 'three';
 import type { PierModel } from '../core/geometry';
 import { assemblyEndOffset, assemblyJs, b10Levels, b9Bars, FOOTING_DEFAULTS, gridPositions, grid, layers, legLength, legOffsets, sideDepth } from '../core/rebar/footing';
-import { bottomPiece, MAIN, widthLayout } from '../core/rebar/coping-main';
+import { bottomPiece, MAIN, topSplicePieces, widthLayout } from '../core/rebar/coping-main';
 import { C14_INSET, c14Bars, CAP, COPING_REBAR, SHEAR_LOOP_STEP, shearBars, shearBarsMulti, shearUHeight, copingSideBars, SIDE_HOOK_LEG, stairBars, undersideAt } from '../core/rebar/coping';
 import { sideRowLevels } from '../core/coping-geom';
 import { columnRebar, columnInputFor, COLUMN_P1 } from '../core/rebar/column';
@@ -152,8 +152,17 @@ export function buildRebar3D(m: PierModel, common: Material = DEFAULT_MATERIAL,
     for (let k = 1; k <= 3; k++) {
       const z = topEl - 0.127 - (k - 1) * (m.copingRebar.mainLayerGap / 1000);
       const xk = cover + ((k - 1) * MAIN.layHorizontal) / 1000;
+      // 상면 이음 (승인 2026-10-26): when applied and longer than the standard, the bar is two pieces overlapping by l_s at the split.
+      const sp = m.topSplice.mode === 'apply' ? topSplicePieces(L * 1000, k, m.topSplice.at, mCoping) : null;
+      const splitX = sp ? xk + (sp.splitFromLeft - MAIN.hook) / 1000 : 0;
+      const half = sp ? sp.lap / 2000 : 0;
       xs.forEach((n, j) => {
         const name = `C${k + (j % 2 === 1 ? 0 : 3)}`;
+        if (sp) {
+          addPath(name, 0, [[xk, z - hookTop, n], [xk, z, n], [splitX + half, z, n]], NOMINAL_DIAMETER.H29, COLOR.coping);
+          addPath(name, 0, [[splitX - half, z, n], [L - xk, z, n], [L - xk, z - hookTop, n]], NOMINAL_DIAMETER.H29, COLOR.coping);
+          return;
+        }
         const pts: [number, number, number][] = [
           [xk, z - hookTop, n],
           [xk, z, n],