fix(viewer): add spacing between callout and columns blocks

## Description

In the CLI Viewer, a callout block placed immediately above a columns block has no visible vertical spacing. The callout's bottom border touches the top edge of the columns container, so the two blocks look visually stuck together.

## Expected behavior

Add a consistent vertical margin or block gap between adjacent callout and columns blocks, matching the spacing used between other document blocks.

## Reproduction

1. Open a document in the CLI Viewer.
2. Place a callout block immediately before a two-column block.
3. Observe the boundary between the callout and the columns container.

## Environment

- Univer CLI: `0.5.0-insider.20260826-4d4b6be`
- Surface: local CLI Viewer

Start in the CLI Viewer code by locating the rendering paths for callout and columns blocks, then compare their spacing with other adjacent document blocks. Reproduce the issue with a callout immediately before a two-column block. Done means the callout border no longer touches the columns container and the spacing is consistent with other blocks.

Written by the indexing model from the issue text.