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/components/admin/offers/OfferEditorClient.tsx

@@ -45,12 +45,15 @@ function formatUnitPrice(raw: string): string {
   return `€${(isNaN(num) ? 0 : num).toLocaleString("it-IT", { minimumFractionDigits: 2, maximumFractionDigits: 2 })}`;
 }
 
+type OfferType = "una_tantum" | "retainer";
+
 type MacroFields = {
   internal_name: string;
   public_name: string;
   description: string;
   category: string | null;
   ticket: string | null;
+  offer_type: OfferType;
   cliente_ideale: string;
   risultato: string;
   tempo: string;
@@ -75,6 +78,7 @@ export function OfferEditorClient({
     description: data.macro.description ?? "",
     category: data.macro.category,
     ticket: data.macro.ticket,
+    offer_type: (data.macro.offer_type === "retainer" ? "retainer" : "una_tantum") as OfferType,
     cliente_ideale: data.macro.cliente_ideale ?? "",
     risultato: data.macro.risultato ?? "",
     tempo: data.macro.tempo ?? "",
@@ -166,6 +170,7 @@ export function OfferEditorClient({
       description: macro.description,
       category: macro.category ?? undefined,
       ticket: macro.ticket ?? undefined,
+      offer_type: macro.offer_type,
       cliente_ideale: macro.cliente_ideale,
       risultato: macro.risultato,
       tempo: macro.tempo,
@@ -319,6 +324,29 @@ export function OfferEditorClient({
           />
         </div>
 
+        <div className="flex items-center gap-3">
+          <span className="text-xs text-[#71717a] w-24 shrink-0">Modalità</span>
+          <div className="inline-flex rounded-lg border border-[#e5e7eb] bg-[#fafafa] p-0.5">
+            {([
+              { value: "una_tantum", label: "Una tantum" },
+              { value: "retainer", label: "Retainer" },
+            ] as const).map((opt) => (
+              <button
+                key={opt.value}
+                type="button"
+                onClick={() => updateMacro("offer_type", opt.value)}
+                className={`px-3 py-1 text-sm rounded-md transition-colors ${
+                  macro.offer_type === opt.value
+                    ? "bg-[#1A463C] text-white font-medium"
+                    : "text-[#71717a] hover:text-[#1a1a1a]"
+                }`}
+              >
+                {opt.label}
+              </button>
+            ))}
+          </div>
+        </div>
+
         <div className="flex items-center gap-3">
           <span className="text-xs text-[#71717a] w-24 shrink-0">Tipo</span>
           <OptionMultiSelect