dsh-excel-panel: DSH Web right sidebar Excel editing plugin

dsh-excel-panel is a right sidebar plugin for DSH Web designed to allow users to preview, edit, and save .xlsx files directly within the DSH Web interface without switching to external tools. The plugin supports cell selection and text editing, offers formatting tools such as font size, bold, alignment, and color adjustment, and includes a real-time formula preview covering common calculations and functions like SUM and IF. Additionally, it supports operations such as merging cells, inserting and deleting rows and columns, adjusting row height and column width, and managing worksheets. In terms of the save mechanism, the plugin rebuilds the entire xlsx file to prevent style corruption, ensuring formatting is preserved after multiple saves, and supports undo and redo. When installing, ensure the environment meets the version requirements for dsh-better-sidebar, React, and exceljs, and it can be accessed via D.