feat: offer_type (una tantum/retainer), dedup tiers, redesigned Offerte tab

- offer_macros.offer_type ('una_tantum'|'retainer') + editor "Modalità" toggle
  (migration 0012, applied to prod)
- migration 0012 also adds UNIQUE(macro_id, tier_letter) — prevents duplicate
  tiers; ran after a one-time dedup of Web Domination's duplicate A/B/C tiers
- OffersTab redesigned: two-step assign (Offer → Tier cards with price), type
  badge "Una tantum/Ricorrente" instead of misleading "X mesi", no redundant
  "· A" when public_name == tier letter, cleaner active-offers cards
- getProjectFullDetail: availableMicros grouped by macro + defensive dedup;
  projectOffers/availableMicros carry offer_type/category/price
- proposal deck PricingSection shows offer type (fallback to duration for
  pre-existing proposals)

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

src/db/schema.ts

@@ -279,6 +279,7 @@ export const offer_macros = pgTable("offer_macros", {
   description: text("description"), // short description shown on offer cards
   category: text("category"), // single-select "Categoria" (Entry/Signature/Retainer Offer) — OFFER-15/18
   ticket: text("ticket"), // single-select "Ticket" (Low/Mid/High Ticket) — OFFER-15
+  offer_type: text("offer_type").notNull().default("una_tantum"), // una_tantum | retainer (v2.3)
   is_archived: boolean("is_archived").notNull().default(false), // OFFER-18 archive flag
   cliente_ideale: text("cliente_ideale"), // "Aiuto: [Cliente Ideale]"
   risultato: text("risultato"), // "A ottenere: [Risultato]"