feat(ui): Select primitive; restyle ProfileSelector on tokens

- New Select primitive in @trails-cool/ui: token-styled native <select>
  (appearance-none + overlaid chevron for a consistent closed control),
  sm/md sizes, sibling of Input. Unit-tested + added to /dev/ui.
- ProfileSelector uses Select (size sm) with token label; the profile
  label now hides on small screens. Completes the topbar's migration
  onto the design system.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/ui/src/index.ts

@@ -7,6 +7,8 @@ export { Card } from "./Card.tsx";
 export type { CardProps } from "./Card.tsx";
 export { Input } from "./Input.tsx";
 export type { InputProps } from "./Input.tsx";
+export { Select } from "./Select.tsx";
+export type { SelectProps, SelectSize } from "./Select.tsx";
 export { IconButton } from "./IconButton.tsx";
 export type {
   IconButtonProps,