feat(rebar): 단면·폐합 at two fixed stations side by side (단부 0.3 m, first column centre)

- The station input is removed. The section shows the 단부 (first shear
  station, from the 3D bar records) and the first column centre, side by side.
- The 상면 간격 label is removed.

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

src/view/coping-rebar-svg.ts

@@ -53,6 +53,12 @@ export function chainDims(positions: number[], startMm: number, endMm: number):
   return out;
 }
 
+/** The 단부 station (m): the first station of the 전단·띠 bars (C9–C11), i.e. the first shear position. */
+export function copingEndStation(records: BarRecord[]): number {
+  const loops = records.filter((r) => /^C(9|10|11)$/.test(r.name));
+  return Math.min(...loops.flatMap((r) => r.pts.map((p) => p[0])));
+}
+
 /**
  * Bar positions (mm, along the coping): one per bar, its mean s. A loop or a cross bar sits at one station, so its
  * points share the same s apart from the bends; the bends are not positions of their own.
@@ -221,7 +227,6 @@ export function copingSectionSvg(records: BarRecord[], s0: number, copingTopEl?:
   for (const d of topChain) {
     parts.push(`<line x1="${d.from}" y1="${dimTop}" x2="${d.to}" y2="${dimTop}" stroke="#18212B" stroke-width="8"></line><text x="${(d.from + d.to) / 2}" y="${dimTop - 90}" text-anchor="middle" font-size="160" fill="#18212B">${d.text}</text>`);
   }
-  parts.push(`<text x="${(-halfW + halfW) / 2}" y="${dimTop - 260}" text-anchor="middle" font-size="150" fill="#55606E">상면 간격</text>`);
 
   // 4: the side rows (C12·C13) along the EL, from the coping top EL down to the lowest side bar.
   const side = unique.filter((c) => c.group === 'side' && c.x < 0);