fix(ui): Keep the Select chevron at the right edge with a custom value (#67)

Select only wrapped its default label in the flex-filling value span, so a
renderValue (the data source Color picker's swatch + name) left the chevron
right after the text, short of the field's edge.

Claude-Session: https://claude.ai/code/session_01VUYsdXA2nkF5v6zsC93dpn

src/ui/Select.tsx

@@ -107,7 +107,7 @@ export function Select<V extends string = string>({
         }}
       >
         {renderValue ? (
-          renderValue(current)
+          <span className={styles.value}>{renderValue(current)}</span>
         ) : (
           <>
             {current?.icon && <Icon name={current.icon} size={14} />}