fix: flag A/B/C persistence, catalog sort+reorder, offer category pools

- Fix duplicate tier INSERT bug (useState not syncing after router.refresh)
- Add column sort by clicking headers in service catalog
- Add drag-and-drop column reordering (persisted in localStorage)
- Add Categorie Offerta section in Impostazioni (tipo/obiettivo/categoria pools)

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

src/app/admin/impostazioni/actions.ts

@@ -0,0 +1,33 @@
+"use server";
+
+import { getJsonPool, updateJsonPool, SETTINGS_KEYS } from "@/lib/settings";
+import { revalidatePath } from "next/cache";
+
+type PoolName = "tipo" | "obiettivo" | "categoria";
+
+function poolKey(pool: PoolName): string {
+  switch (pool) {
+    case "tipo":      return SETTINGS_KEYS.OFFER_TIPO_POOL;
+    case "obiettivo": return SETTINGS_KEYS.OFFER_OBIETTIVO_POOL;
+    case "categoria": return SETTINGS_KEYS.OFFER_CATEGORIA_POOL;
+  }
+}
+
+export async function addPoolValue(pool: PoolName, value: string): Promise<void> {
+  const trimmed = value.trim();
+  if (!trimmed) return;
+  const key = poolKey(pool);
+  const current = await getJsonPool(key);
+  if (current.includes(trimmed)) return;
+  await updateJsonPool(key, [...current, trimmed]);
+  revalidatePath("/admin/impostazioni");
+  revalidatePath("/admin/offers");
+}
+
+export async function removePoolValue(pool: PoolName, value: string): Promise<void> {
+  const key = poolKey(pool);
+  const current = await getJsonPool(key);
+  await updateJsonPool(key, current.filter((v) => v !== value));
+  revalidatePath("/admin/impostazioni");
+  revalidatePath("/admin/offers");
+}