fix(web): give the protocol dropdowns the shared chevron

`select.input` caps the control at 240px, and a `<select>` carrying only
`.input` keeps the OS arrow, which paints flush inside that shrunk right
edge — visibly tighter than every other control on the page. Both
protocol dropdowns took `.input` alone; the provider select beside them
already added `.selectInput`, which removes the OS arrow, reserves the
right pad, and paints the shared 12px chevron.

The stylesheet spec now reads the package's own sources and fails any
`<select>` that takes `.input` without `.selectInput`, so the next one
cannot be added bare.

packages/client/ui-models/src/client/CustomProviderCard.tsx

@@ -236,7 +236,7 @@ export function CustomProviderCard(props: CustomProviderCardProps): ReactNode {
       <div className={styles['field']}>
         <span className={styles['fieldLabel']}>{t('customApi')}</span>
         <select
-          className={styles['input']}
+          className={`${styles['input']} ${styles['selectInput']}`}
           value={protocol}
           aria-label={t('customApi')}
           disabled={profileDisabled}

packages/client/ui-models/src/client/ProviderEditor.tsx

@@ -396,7 +396,7 @@ export function ProviderEditor(props: ProviderEditorProps): ReactNode {
                 <div className={styles['field']}>
                   <span className={styles['fieldLabel']}>{t('customApi')}</span>
                   <select
-                    className={styles['input']}
+                    className={`${styles['input']} ${styles['selectInput']}`}
                     value={probeApi ?? ''}
                     aria-label={t('customApi')}
                     disabled={disabled}