fix(renderer): make ScrollBox defaults sane

[re-marked]

Summary

• Default <ScrollBox> layout to flexDirection: 'column' so normal vertical lists/logs produce scrollable content without a workaround.
• Clamp scrollTo and scrollBy targets to [0, scrollHeight - viewportHeight] while preserving the existing pending-delta drain path for smooth wheel scrolling.
• Add ScrollBox regression tests and update ScrollBox docs/changelog notes.

Closes #54.
Closes #74.

Verification

• pnpm test -- packages/renderer/src/components/ScrollBox.test.tsx
• pnpm --filter @yokai-tui/renderer typecheck
• pnpm --filter @yokai-tui/renderer lint
• pnpm --filter @yokai-tui/renderer build
• git diff --check

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve requested scrolls until fresh layout bounds exist

When this runs before the first renderer pass or immediately after children grow, scrollHeight and scrollViewportHeight are still unset or stale because the renderer refreshes them later in render-node-to-output. Clamping here makes mount-time scrollTo(10) collapse to 0 and can truncate scrollBy during the same commit to the old max, so the later render no longer has the caller's requested target to clamp against fresh Yoga bounds; before this change the requested offset/delta survived until render-time clamping.

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