Raise exception on spreadsheet errors instead of silently skipping

**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>

services/sheets_service.py

@@ -315,11 +315,19 @@ class SheetsService:
 
                     # Check for spreadsheet errors
                     if self._is_spreadsheet_error(value):
-                        self.logger.warning(
-                            f"Row {row_num}: Spreadsheet error '{value}' in field '{field_name}' - skipping row"
+                        raise SheetsException(
+                            f"❌ Spreadsheet Error Detected\n\n"
+                            f"**Location:** Row {row_num}, Column '{field_name}'\n"
+                            f"**Value Found:** `{value}`\n\n"
+                            f"This cell contains a formula error that must be fixed before submission.\n\n"
+                            f"**Common Error Types:**\n"
+                            f"• `#REF!` - Invalid cell reference (deleted row/column)\n"
+                            f"• `#N/A` - Lookup formula couldn't find a match\n"
+                            f"• `#VALUE!` - Wrong data type in formula\n"
+                            f"• `#DIV/0!` - Division by zero\n"
+                            f"• `#NAME?` - Unrecognized formula name\n\n"
+                            f"**Action Required:** Fix cell {field_name} in row {row_num} and resubmit."
                         )
-                        has_error = True
-                        break
 
                     # Sanitize integer fields
                     if field_name in int_fields: