CedarCopilot/cedar-mail

Branch: staging

fix(kb): let the Drive picker offer Excel, CSV and Sheets files

merged#2930CedarCopilot

CedarCopilot wants to merge 2 commits into staging from worktree-send-it-drive-picker-excel

What Libra verified

Linked spreadsheets appear with spreadsheet icons and usable viewer links
Libra ran this behavior against the change and confirmed the check detects when it breaks.
Technical evidence
- linked native Sheets and XLSX files remain visible with spreadsheet icons and their correct viewer links
Changed code: google-slides-manager.tsx.