feat(preview): Add interactive SplitButtonPreview component

[Copilot]

Replaces the static HTML code block and LiveEditorCompact on the Split-Button docs page with a fully interactive SplitButtonPreview component, consistent with other component preview migrations.

Changes

• src/components/previews/components/SplitButton.tsx — New preview component using the slot pattern (popover content rendered via sanitized dangerouslySetInnerHTML). Exposes _label, _variant, _tooltipAlign, _icons, _disabled, _hideLabel, and _slot (popover content) as interactive properties.

• docs/30-components/split-button.mdx / i18n/en/.../split-button.mdx — Replaced static <kol-split-button> example and <LiveEditorCompact> with two <SplitButtonPreview> instances (one with full property panel in the Construction section, one minimal in the Example section). Added # API heading above <Readme />. Removed tags frontmatter and old imports.

• i18n/de/code.json / i18n/en/code.json — Added preview.component.split-button.label and preview.component.split-button.slot translation keys.

<SplitButtonPreview
  visibleProperties={['_label', '_variant', '_tooltipAlign', '_icons', '_disabled', '_hideLabel', '_slot']}
  codeCollapsable
  codeCollapsed
/>

[github-actions]

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