fix(editor): stretch latex preview content (#14857)

### Summary of Changes
Resolves #13340. Change align-items to stretch to full width to avoid
tag/label from overlapping with equation.

### Screenshot Verification
**Before**
<img width="661" height="256" alt="Screenshot 2026-04-19 at 5 58 03 PM"
src="https://github.com/user-attachments/assets/a99d0138-838f-4f91-bd63-cbd07710484c"
/>

**After**
<img width="614" height="275" alt="Screenshot 2026-04-19 at 5 58 16 PM"
src="https://github.com/user-attachments/assets/7e62ab09-f290-4b6e-9cd6-d20b8f990da3"
/>

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Style**
* Improved the vertical alignment of LaTeX block content to better
utilize container space.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/blocks/latex/src/styles.ts

@@ -9,7 +9,7 @@ export const latexBlockStyles = css`
     height: 100%;
     padding: 10px 24px;
     flex-direction: column;
-    align-items: center;
+    align-items: stretch;
     justify-content: center;
     border-radius: 4px;
     overflow-x: auto;