fix: prevent horizontal overflow on mobile portal pages

- PetProfiles.tsx: add flex-shrink-0 to tab row to prevent collapse underflow
- BillingPayments.tsx: add flex-shrink-0 to tab button row

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/src/portal/sections/BillingPayments.tsx

@@ -130,7 +130,7 @@ function BillingPaymentsInner({ sessionId, readOnly }: BillingPaymentsProps) {
         </div>
       )}
 
-      <div className="flex gap-2 flex-wrap">
+      <div className="flex gap-2 flex-wrap flex-shrink-0">
         {([
           { id: "invoices" as const, label: "Invoices", icon: DollarSign },
           { id: "payment" as const, label: "Payment Methods", icon: CreditCard },

apps/web/src/portal/sections/PetProfiles.tsx

@@ -182,7 +182,7 @@ export function PetProfiles({ sessionId, readOnly }: Props) {
       )}
 
       {/* Tabs */}
-      <div className="flex gap-1 bg-white rounded-xl border border-stone-200 p-1 overflow-x-auto">
+      <div className="flex gap-1 bg-white rounded-xl border border-stone-200 p-1 overflow-x-auto flex-shrink-0">
         {([
           { id: "info", label: "Basic Info", icon: PawPrint },
           { id: "medical", label: "Medical", icon: Heart },