feat: Use nullish coalescing for default select values

Replaces `||` with `??` for more precise default value assignment in select components.

Also updates Vite config to set `base` to `/` and disable sourcemaps during build.

components/AccountsReceivableView.tsx

@@ -358,7 +358,7 @@ export const AccountsReceivableView: React.FC<AccountsReceivableViewProps> = ({
                 <div>
                   <label className="block text-sm font-bold text-slate-800 mb-1">Categoria</label>
                   <CustomSelect 
-                    value={newReceivable.category || 'Serviços'}
+                    value={newReceivable.category ?? 'Serviços'}
                     onChange={(val) => setNewReceivable({...newReceivable, category: val})}
                     options={[
                         { value: 'Serviços', label: 'Serviços' },
@@ -371,7 +371,7 @@ export const AccountsReceivableView: React.FC<AccountsReceivableViewProps> = ({
                 <div>
                   <label className="block text-sm font-bold text-slate-800 mb-1">Tipo</label>
                   <CustomSelect 
-                    value={newReceivable.type}
+                    value={newReceivable.type ?? 'one-time'}
                     onChange={(val) => setNewReceivable({...newReceivable, type: val})}
                     options={[
                         { value: 'one-time', label: 'Avulso' },