Fix bugs and improve pipeline flexibility

- Fix gpu_cleanup import missing in visualizations.py (NameError in workers)
- Fix t_pdf referenced before assignment when PDF is skipped
- Skip classification+DTM when DTM exists regardless of --force
- --force now only regenerates WebP/PDF, not classification/DTM
- --force-classification forces reclassification when needed
- Add laspy repair fallback for corrupt LAZ files (EVLR errors)
- Keep DTM TIF by default for reuse (--no-keep-tif to delete)
- Increase space between image and bottom cartouche (0.12→0.19)

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

lidar_pipeline/cli.py

@@ -118,9 +118,9 @@ Exemples:
         help="Reclassifier le sol même si le fichier .las existe déjà"
     )
     parser.add_argument(
-        "--keep-tif",
+        "--no-keep-tif",
         action="store_true",
-        help="Conserver les fichiers TIFF intermédiaires (sinon supprimés après conversion WebP)"
+        help="Supprimer les fichiers TIFF intermédiaires après conversion WebP (par défaut: conservés)"
     )
     parser.add_argument(
         "--ground-classification",
@@ -176,7 +176,7 @@ Exemples:
             force=args.force,
             ground_method=args.ground_classification,
             force_classify=args.force_classification,
-            keep_tif=args.keep_tif,
+            keep_tif=not args.no_keep_tif,
         )
 
         # If --file is specified, process only matching files