fix: export job records display shows files instead of mixed metrics

Previously export jobs showed "3/23" (languages/products) which was confusing.
Now shows "3/3" (files succeeded / files processed) for consistency.

- Updated log_export to track files_processed/succeeded/failed
- Products count stored in error_details for reference
- Updated documentation to explain records column meaning per job type

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/guides/letzshop-admin-management.md

@@ -155,10 +155,19 @@ Each job displays:
 - **ID**: Unique job identifier
 - **Type**: Import, Export, Historical Import, or Order Sync
 - **Status**: Pending, Processing, Completed, Failed, or Partial
-- **Records**: Success count / Total processed (failed count)
+- **Records**: Success count / Total processed (failed count if any)
 - **Started**: When the job began
 - **Duration**: How long the job took
 
+#### Records Column Meaning
+
+| Job Type | Records Shows |
+|----------|---------------|
+| Product Import | Products imported / Total products |
+| Product Export | Files exported / Total files (3 languages) |
+| Historical Import | Orders imported / Total orders |
+| Order Sync | Orders synced / Total orders |
+
 ### Filtering
 
 - **Type Filter**: Show specific job types