feat: centralized Notion-style taxonomy management in settings

Single persistent option pool per taxonomy (7 fields: offer
categoria/ticket/tipo/obiettivo + catalog fase/offerta/pacchetto),
stored as JSON in the settings table (no DB migration).

- src/lib/taxonomy.ts: pools with lazy seed from in-use values,
  add/remove(cascade)/rename helpers
- Inline creation anywhere registers into the pool (save offer,
  addServiceOption, updateServiceField fase, quickAdd, create macro)
- Deselecting on a row never touches the pool; global delete only
  from settings (cascade-strips tags / nulls columns)
- getOfferFieldOptions + getCatalogFieldOptions read from pools
- Settings: TaxonomyManager (offer + catalog groups), confirm on delete

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/admin/impostazioni/page.tsx

@@ -1,15 +1,11 @@
-import { getTargetHourlyRate, getJsonPool, updateSetting, SETTINGS_KEYS } from "@/lib/settings";
-import { OfferPoolsSection } from "@/components/admin/impostazioni/OfferPoolsSection";
+import { getTargetHourlyRate, updateSetting, SETTINGS_KEYS } from "@/lib/settings";
+import { getAllPools } from "@/lib/taxonomy";
+import { TaxonomyManager } from "@/components/admin/impostazioni/TaxonomyManager";
 
 export const revalidate = 0;
 
 export default async function ImpostazioniPage() {
-  const [targetRate, tipoPool, obiettivoPool, categoriaPool] = await Promise.all([
-    getTargetHourlyRate(),
-    getJsonPool(SETTINGS_KEYS.OFFER_TIPO_POOL),
-    getJsonPool(SETTINGS_KEYS.OFFER_OBIETTIVO_POOL),
-    getJsonPool(SETTINGS_KEYS.OFFER_CATEGORIA_POOL),
-  ]);
+  const [targetRate, pools] = await Promise.all([getTargetHourlyRate(), getAllPools()]);
 
   async function handleSave(fd: FormData) {
     "use server";
@@ -62,11 +58,7 @@ export default async function ImpostazioniPage() {
           </form>
         </div>
 
-        <OfferPoolsSection
-          tipoPool={tipoPool}
-          obiettivoPool={obiettivoPool}
-          categoriaPool={categoriaPool}
-        />
+        <TaxonomyManager pools={pools} />
       </div>
     </div>
   );