feat(view,rebar): column diameter D as a free input on ② (1200–3000 mm, 50 mm steps), with three checks

D is an input on the column card (default 2000 mm). The 3D column, the piles of a cast-in pier and the column rebar follow it;
n_div stays 46. Three checks run on each regenerate and appear in 알림: D below the Level width (2100), D + 2c within the
coping width, and the 주철근 arc spacing ≥ max(1.5·d_b, 40). Spec §5.2 records the rule (approved 2026-10-23).

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

src/core/rebar/column.ts

@@ -54,7 +54,7 @@ export function columnInputFor(model: PierModel, base: ColumnInput = COLUMN_P1):
   const eP1 = Math.round((seg.top - (c3 - 0.1)) * 1000);
   // e_top: the coping middle level (Level 하면 + 계단 상면)/2 is the top of P3 and P6 (승인 2026-10-23).
   const eTop = Math.round((seg.top - (model.levelBottom + seg.top) / 2) * 1000);
-  return { ...base, Hc, hcop, eP1, eTop };
+  return { ...base, Hc, hcop, eP1, eTop, D: model.columnDiameterMm };
 }
 
 export const COLUMN_P1: ColumnInput = {