fix: fix optional google sheet sharing

[stevenle]

Summary

This PR makes Google Sheet sharing optional during export and improves error handling when sharing fails. The sharing operation is now wrapped in a try-catch block so that sheet creation succeeds even if sharing encounters an error.

Key Changes

• Conditional sharing logic: Inverted the share condition to only attempt sharing when explicitly requested, rather than sharing by default
• Error handling: Wrapped the sharing operation in a try-catch block that logs a warning if sharing fails, allowing the sheet to remain usable
• UI fix: Changed the share checkbox from a controlled component using checked prop to an uncontrolled component using defaultChecked for proper React patterns

Implementation Details

• The sharing operation now gracefully degrades — if it fails, users can manually share the sheet later
• The checkbox state is now properly managed as an uncontrolled component, which is more appropriate for this use case
• Console warning is logged when sharing fails to help with debugging while not blocking the user's workflow

https://claude.ai/code/session_01Woi52LoFphT663pRrUiNDF