StepUpload was showing hardcoded "42 Total Lines, 8 Display Formats"
for every file upload. Now:
- Added POST /jobs/validate-source endpoint that parses xlsx in a
temp file and returns real stats (line count, display formats,
columns found, warnings) without creating any DB records
- Frontend calls validateSource() when user selects a file
- Shows spinner during validation, real results after
- Blocks "Next" if validation fails
- Removed all mock validation data
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
b11b2df0e2