refactor: move shared utilities to lib/shared/ sub-packages

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/person/personLifeDates.ts

@@ -0,0 +1,20 @@
+/**
+ * Formats the life date range for a person.
+ * Examples:
+ *   * 1882 – † 1944  (both)
+ *   * 1882            (birth only)
+ *   † 1944            (death only)
+ *   ""                (neither)
+ */
+export function formatLifeDateRange(birthYear?: number | null, deathYear?: number | null): string {
+	if (birthYear && deathYear) {
+		return `* ${birthYear} – † ${deathYear}`;
+	}
+	if (birthYear) {
+		return `* ${birthYear}`;
+	}
+	if (deathYear) {
+		return `† ${deathYear}`;
+	}
+	return '';
+}