[FR]: Add code example to Spinner.md

Describe the problem

Spinner.md describes intents and sizes but has no code example. A reader cannot use the component from this doc alone.

Describe the solution

Add a minimal usage snippet:

Spinner(intent = SpinnerIntent.Main)
Spinner(intent = SpinnerIntent.Current, size = SpinnerSize.Small)

Additional context

Priority: Medium. Effort: XS.