Improve Table Editor to match Confluence's usability (insert rows/columns, colors, etc.)

Description: Is your feature request related to a problem? Please describe. Currently, the table editing experience in Outline is quite basic and rigid compared to other modern documentation tools like Confluence. When editing a document (as shown in the attached screenshot), it is difficult to quickly modify the table structure. Common actions like inserting a new row/column or deleting a specific row/column are not easily accessible, often requiring workarounds. Furthermore, the lack of cell styling options (such as background colors for headers or specific cells) limits the ability to create well-organized and visually readable documents. Additionally, after merging cells (rows or columns), the ability to add or delete rows within the merged area becomes very unfriendly and cumbersome. It would be greatly appreciated if the editor could handle row/column insertion and deletion more gracefully within merged cells. <img width="964" height="422" alt=&quo…