refactor: extract shared string normalization helpers

src/shared/string-normalization.ts

@@ -0,0 +1,17 @@
+export function normalizeStringEntries(list?: Array<string | number>) {
+  return (list ?? []).map((entry) => String(entry).trim()).filter(Boolean);
+}
+
+export function normalizeStringEntriesLower(list?: Array<string | number>) {
+  return normalizeStringEntries(list).map((entry) => entry.toLowerCase());
+}
+
+export function normalizeHyphenSlug(raw?: string | null) {
+  const trimmed = raw?.trim().toLowerCase() ?? "";
+  if (!trimmed) {
+    return "";
+  }
+  const dashed = trimmed.replace(/\s+/g, "-");
+  const cleaned = dashed.replace(/[^a-z0-9#@._+-]+/g, "-");
+  return cleaned.replace(/-{2,}/g, "-").replace(/^[-.]+|[-.]+$/g, "");
+}