docs(rebar): record that the side-row levels follow 코핑철근.md §6.1 (z_0 = Level underside + 127)

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

src/core/coping-geom.ts

@@ -15,9 +15,9 @@ export interface CopingGeom {
 export const P1_COPING_GEOM: CopingGeom = { h1: 1000, h2: 1500, levelWidth: 2100 };
 
 /**
- * Side-row levels (EL m) of C12 / C13 from the Level underside: the lowest row and the row where the sloped underside breaks.
- * P1: 40.911 + 0.377 = 41.288 and 40.911 + 1.627 = 42.538. ASSUMPTION: the side rows keep this position relative to the
- * Level underside when h1 or h2 changes (명세 확인 필요).
+ * Side-row levels (EL m) of C12 / C13 from the Level underside. 코핑철근.md §6.1: z_0 = 하면 주철근 Level 높이 = 41.038,
+ * which is the Level underside 40.911 plus 127; z_k = z_0 + k·250, and the break is z_6 = 42.538 (C12 below, C13 above).
+ * So the rows keep this offset from the Level underside.
  */
 export function sideRowLevels(levelBottom: number): { zBottom: number; zBreak: number } {
   return { zBottom: levelBottom + 0.377, zBreak: levelBottom + 1.627 };