- Add umya-spreadsheet v2.3 dependency (preserves charts, styles, images, formulas, macros, comments)
- Rewrite storage.rs to use umya-spreadsheet for read/write
- Keep original workbook in memory during edit session
- On cell edit: modify only that cell via update_xlsx_cell()
- On save: write full workbook via save_workbook_to_drive()
- Preserve all Excel features: merged cells, frozen panes, comments, styles
- Extract cell styles (font, color, background, alignment)
- Parse and preserve merge ranges
- Support formula preservation with = prefix handling
Rodrigo Rodriguez (Pragmatismo)
8a9a913ffb