feat(jobs): introduce extracting_pages status and update job progress handling

- Added a new job status 'extracting_pages' to represent the first sub-phase of thumbnail generation.
- Updated the database schema to include a timestamp for when thumbnail generation starts.
- Enhanced job progress components to handle the new status, including UI updates for displaying progress and status labels.
- Refactored job-related logic to accommodate the two-phase process: extracting pages and generating thumbnails.
- Adjusted SQL queries and job detail responses to include the new fields and statuses.

This change improves the clarity of job processing states and enhances user feedback during the thumbnail generation process.

apps/backoffice/app/components/JobProgress.tsx

@@ -87,8 +87,8 @@ export function JobProgress({ jobId, onComplete }: JobProgressProps) {
   const percent = progress.progress_percent ?? 0;
   const processed = progress.processed_files ?? 0;
   const total = progress.total_files ?? 0;
-  const isThumbnailsPhase = progress.status === "generating_thumbnails";
-  const unitLabel = isThumbnailsPhase ? "thumbnails" : "files";
+  const isPhase2 = progress.status === "extracting_pages" || progress.status === "generating_thumbnails";
+  const unitLabel = progress.status === "extracting_pages" ? "pages" : progress.status === "generating_thumbnails" ? "thumbnails" : "files";
 
   return (
     <div className="p-4 bg-card rounded-lg border border-border">
@@ -112,7 +112,7 @@ export function JobProgress({ jobId, onComplete }: JobProgressProps) {
         )}
       </div>
 
-      {progress.stats_json && !isThumbnailsPhase && (
+      {progress.stats_json && !isPhase2 && (
         <div className="flex flex-wrap gap-3 text-xs">
           <Badge variant="primary">Scanned: {progress.stats_json.scanned_files}</Badge>
           <Badge variant="success">Indexed: {progress.stats_json.indexed_files}</Badge>