fix: prevent negative numeric inputs in rental forms by enforcing positive constraints and sanitizing user entries

src/app/admin/rentals/[id]/page.tsx

@@ -609,8 +609,9 @@ export default function RentalDetailPage() {
               <label className="text-sm text-slate-600">Due Amount (৳)</label>
               <input
                 type="number"
+                min={0}
                 value={dueAmount}
-                onChange={(e) => setDueAmount(Number(e.target.value))}
+                onChange={(e) => setDueAmount(Math.max(0, Number(e.target.value)))}
                 className="w-full px-3 py-2 border border-slate-200 rounded-lg text-sm mt-1"
                 placeholder="Enter amount..."
               />