feat: add rescan job type and improve full rebuild UX

Add "Deep rescan" job type that clears directory mtimes to force
re-walking all directories, discovering newly supported formats (e.g.
EPUB) without deleting existing data or metadata.

Also improve full rebuild button: red destructive styling instead of
warning, and FR description explicitly mentions metadata/reading status
loss. Rename FR rebuild label to "Mise à jour".

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/backoffice/lib/i18n/en.ts

@@ -186,6 +186,7 @@ const en: Record<TranslationKey, string> = {
   "jobs.startJobDescription": "Select a library (or all) and choose the action to perform.",
   "jobs.allLibraries": "All libraries",
   "jobs.rebuild": "Rebuild",
+  "jobs.rescan": "Deep rescan",
   "jobs.fullRebuild": "Full rebuild",
   "jobs.generateThumbnails": "Generate thumbnails",
   "jobs.regenerateThumbnails": "Regenerate thumbnails",
@@ -198,12 +199,14 @@ const en: Record<TranslationKey, string> = {
   "jobs.groupMetadata": "Metadata",
   "jobs.requiresLibrary": "Requires a specific library",
   "jobs.rebuildShort": "Scan new & modified files",
+  "jobs.rescanShort": "Re-walk all directories to discover new formats",
   "jobs.fullRebuildShort": "Delete all & re-scan from scratch",
   "jobs.generateThumbnailsShort": "Missing thumbnails only",
   "jobs.regenerateThumbnailsShort": "Recreate all thumbnails",
   "jobs.batchMetadataShort": "Auto-match unlinked series",
   "jobs.refreshMetadataShort": "Update existing linked series",
   "jobs.rebuildDescription": "Incremental scan: detects files added, modified, or deleted since the last scan, indexes them, and generates missing thumbnails. Existing unmodified data is preserved. This is the most common and fastest action.",
+  "jobs.rescanDescription": "Re-walks all directories regardless of whether they changed, discovering files in newly supported formats (e.g. EPUB). Existing books and metadata are fully preserved — only genuinely new files are added. Slower than a rebuild but safe for your data.",
   "jobs.fullRebuildDescription": "Deletes all indexed data (books, series, thumbnails) then performs a full scan from scratch. Useful if the database is out of sync or corrupted. Long and destructive operation: reading statuses and manual metadata will be lost.",
   "jobs.generateThumbnailsDescription": "Generates thumbnails only for books that don't have one yet. Existing thumbnails are not affected. Useful after an import or if some thumbnails are missing.",
   "jobs.regenerateThumbnailsDescription": "Regenerates all thumbnails from scratch, replacing existing ones. Useful if thumbnail quality or size has changed in the configuration, or if thumbnails are corrupted.",
@@ -310,6 +313,7 @@ const en: Record<TranslationKey, string> = {
 
   // Job types
   "jobType.rebuild": "Indexing",
+  "jobType.rescan": "Deep rescan",
   "jobType.full_rebuild": "Full indexing",
   "jobType.thumbnail_rebuild": "Thumbnails",
   "jobType.thumbnail_regenerate": "Regen. thumbnails",
@@ -318,6 +322,8 @@ const en: Record<TranslationKey, string> = {
   "jobType.metadata_refresh": "Refresh meta.",
   "jobType.rebuildLabel": "Incremental indexing",
   "jobType.rebuildDesc": "Scans new/modified files, analyzes them, and generates missing thumbnails.",
+  "jobType.rescanLabel": "Deep rescan",
+  "jobType.rescanDesc": "Re-walks all directories to discover files in newly supported formats (e.g. EPUB). Existing data is preserved — only new files are added.",
   "jobType.full_rebuildLabel": "Full reindexing",
   "jobType.full_rebuildDesc": "Deletes all existing data then performs a full scan, re-analysis, and thumbnail generation.",
   "jobType.thumbnail_rebuildLabel": "Thumbnail rebuild",