**Problem:**
The _is_spreadsheet_error() check was logging a warning and silently skipping
rows with formula errors (#REF!, #N/A, etc.). This could lead to incomplete
game data being submitted without the user knowing.
**Solution:**
Raise SheetsException immediately when spreadsheet errors are detected,
providing:
- Exact row number and field name
- Actual error value found in the cell
- Common error type explanations
- Clear action required to fix
**Impact:**
- Users get immediate feedback about spreadsheet errors
- No partial/incomplete data submitted to API
- Clear instructions on what needs to be fixed
- Better data integrity
**Example Error Message:**
```
❌ Spreadsheet Error Detected
**Location:** Row 7, Column 'pitcher_id'
**Value Found:** `#REF!`
This cell contains a formula error that must be fixed before submission.
**Action Required:** Fix cell pitcher_id in row 7 and resubmit.
```
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
