feat(core): parse P1 workbook and build T-type pier shape

- parse Excel input by header strings (pier, IP, bearing tables)
- DMS azimuth parser (E03), input validation (E01, E02)
- pure geometry: axis, bearings, stepped coping, column, footing, piles, blinding
- warnings W01, W02, W05, W07, I01
- regression tests against spec.md section 12 (P1)

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

src/core/dms.ts

@@ -0,0 +1,12 @@
+const DMS = /(\d+(?:\.\d+)?)°\s*(\d+)'\s*(\d+(?:\.\d+)?)"/;
+
+/** Parses a degree-minute-second string such as ` 75°56'55.9"` into decimal degrees. Returns null when invalid. */
+export function parseDms(text: string): number | null {
+  const m = DMS.exec(String(text));
+  if (!m) return null;
+  const deg = Number(m[1]);
+  const min = Number(m[2]);
+  const sec = Number(m[3]);
+  if (min >= 60 || sec >= 60) return null;
+  return deg + min / 60 + sec / 3600;
+}