feat(parser): add ISO8601 duration parser

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/server/parsers/iso8601-duration.ts

@@ -0,0 +1,14 @@
+const PATTERN = /^P(?:(\d+)D)?(?:T(?:(\d+)H)?(?:(\d+)M)?(?:(\d+)S)?)?$/;
+
+export function parseIso8601Duration(input: string | null | undefined): number | null {
+  if (typeof input !== 'string' || input.length === 0) return null;
+  if (input === 'P' || input === 'PT') return null;
+  const m = PATTERN.exec(input);
+  if (!m) return null;
+  const [, d, h, min, s] = m;
+  if (!d && !h && !min && !s) return null;
+  const days = d ? parseInt(d, 10) : 0;
+  const hours = h ? parseInt(h, 10) : 0;
+  const mins = min ? parseInt(min, 10) : 0;
+  return days * 24 * 60 + hours * 60 + mins;
+}