feat: mp-3203-add a small size to KvSwitch

[infante-jaime]

https://kiva.atlassian.net/browse/MP-3203

What this does

Adds a size prop to KvSwitch: default and small.

Checkout's tip-from-balance experiment needs a 48×28 switch per design, and KvSwitch hardcoded 56×32 with no way to change it — the consuming app is currently doing it with a scoped :deep override of the component's internals, which is the kind of thing this prop exists to remove.

The prop

Follows the KvButton size pattern: validated string, default | small, computed classes per size.

default — 56×32 track, 24px knob, 24px travel. Byte-for-byte the same classes as before, just moved from the static class attribute into the computed's default branch, so every existing consumer renders unchanged.
small — 48×28 track, 20px knob, 20px travel. The travel is derived from the geometry (track minus knob minus its margins), so the knob sits flush at both ends.
Tests

Both sizes pinned in the spec — including default, so a future change to the stock size fails a test instead of slipping through. The 53 pre-existing failures in unrelated suites are identical on main.

Story

Added a Small story and a size select control. This meant rewriting KvSwitch.stories.js to the modern args pattern (setup() { return { args }; }, as in KvButton.stories.js) — the old Vue 2-style props: Object.keys(argTypes) template was silently ignoring args in the current Storybook, so the existing Disabled story has been rendering an enabled switch. That's fixed as a side effect. The dead checked arg (never a real prop) and the console.log on change were dropped in the rewrite.

Consumer follow-up

Once this publishes, ui swaps its :deep override for size="small" (change already staged there, riding with the version bump).

[roger-in-kiva]

We should probably add documentation using this prompt:
https://github.com/kiva/kv-ui-elements/blob/main/%40kiva/kv-components/docs/ai-documentation-prompt.md

[dyersituations]

Looks good pending using Skill to update docs.

[eddieferrer]

I don't think this is related to this change specifically, but I noticed that the "disabled" functionality is not working:
https://608b4cf87f686c00213841b1-dgkmnopcrj.chromatic.com/?path=/story/forms-kvswitch--disabled

[mcstover]

Seems fine. We should make sure that Design knows about the updates as they are incorporating these into the design system

[cristhianDt]

LGTM , just add the link to the ticket please, or any additional confirmation by design/product team, thanks

[infante-jaime]

I don't think this is related to this change specifically, but I noticed that the "disabled" functionality is not working: https://608b4cf87f686c00213841b1-dgkmnopcrj.chromatic.com/?path=/story/forms-kvswitch--disabled

Hey @eddieferrer, you're right. I just made a quick fix. It was only a Storybook issue, not component-related, so I think it's fine to include it here.

[mcstover]

@infante-jaime Need a small update to the Kitchen Sink story for the disabled state too:
https://www.chromatic.com/test?appId=608b4cf87f686c00213841b1&id=6aa42c87b3b17366c39bcca1

[infante-jaime]

@infante-jaime Need a small update to the Kitchen Sink story for the disabled state too: https://www.chromatic.com/test?appId=608b4cf87f686c00213841b1&id=6aa42c87b3b17366c39bcca1

yes on it TY

[dyersituations]

👍