feat(core,view): footing rebar B1–B12 (plan C5) and the ③ rebar screen v1

- Footing (확대기초철근 (1).md): grid counts from W and L, layer heights,
  B1–B4 and B5–B8 counts and lengths (B2 13646, B6 11396), B10-1/B10-2,
  B11 (60) and B12 (47) with their lengths. B9 is not computed yet.
- rebarSummary: one 철근표 per pier from the model (bearing, coping, column,
  footing), with alerts: RB-F08 (B2 needs a splice, Q-B6), RB-F09 (B9 not
  computed).
- ③ screen v1: stage nav button, member tabs (받침블럭 · 코핑 · 기둥 · 확대기초),
  rebar table with 번호 · 규격 · 개수 · 길이 · 비고, alert list, and the open
  questions (Q-B5, Q-B6, Q-C9). Drawings and the 강조 연동 are not in v1.
- Tests: footing values from the document; P1 summary totals; warnings.
- Not verified in a browser.

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

src/core/rebar/common.ts

@@ -33,6 +33,11 @@ export const NOMINAL_DIAMETER = {
   H29: 28.6,
   S32: 31.8,
   D35: 34.9,
+  /** SD500 names used by the footing document (same nominal diameters). */
+  S16: 15.9,
+  S19: 19.1,
+  S25: 25.4,
+  S29: 28.6,
 } as const;
 
 export type BarSize = keyof typeof NOMINAL_DIAMETER;