Add cálculo de trial y badge de plan

mvp/b2c/src/lib/billing/plan.ts

@@ -0,0 +1,19 @@
+export function trialDaysRemaining(trialEndsAt: Date | null, now: Date = new Date()): number {
+  if (!trialEndsAt) return 0;
+  const ms = trialEndsAt.getTime() - now.getTime();
+  if (ms <= 0) return 0;
+  return Math.ceil(ms / (24 * 60 * 60 * 1000));
+}
+
+export function formatPlanBadge(
+  planNombre: string | null,
+  status: string,
+  trialEndsAt: Date | null,
+  now: Date = new Date()
+): string {
+  const plan = planNombre ? `Plan ${planNombre}` : 'Sin plan';
+  if (status === 'trial') {
+    return `${plan} · trial, ${trialDaysRemaining(trialEndsAt, now)} días restantes`;
+  }
+  return `${plan} · ${status}`;
+}