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>

CLAUDE.md

@@ -17,7 +17,8 @@ All commands run inside Docker. Use `./run.sh` as the primary interface.
 ./run.sh --test                                 # Run unit tests
 ./run.sh -g --file LHD_FXX_1000_6882_PTS_LAMB93_IGN69.copc  # Single file
 ./run.sh --ground-classification pmf            # Force PMF ground classification
-./run.sh -g --keep-tif                          # Keep intermediate TIFF files
+./run.sh -g --keep-tif                          # Keep intermediate TIFF files (default: kept)
+./run.sh -g --no-keep-tif                       # Delete intermediate TIFF files
 ./run.sh                                        # Print help (no args)
 ```
 
@@ -82,6 +83,6 @@ Uses `ProcessPoolExecutor` with `'spawn'` start method (required for CUDA). Each
 - **Language**: UI messages and comments in French. Code identifiers in English.
 - **Logging**: Use `logger = logging.getLogger("lidar")`. Prefix per-file logs via `_file_filter.basename`.
 - **GPU pattern**: `arr_gpu = to_gpu(arr)` → compute → `result = to_cpu(arr_gpu)` → `gpu_cleanup()` between visualizations.
-- **Output format**: Visualizations saved as WebP. TIFF intermediates deleted after conversion unless `--keep-tif`. No COGs or viewer — only WebP + PDF report remain.
+- **Output format**: Visualizations saved as WebP. DTM TIFF kept by default for reuse (use `--no-keep-tif` to delete). `--force` regenerates WebPs without re-classifying if DTM exists. No COGs or viewer — only WebP + PDF report remain.
 - **Compression**: TIF intermediates use `deflate` compression (faster than LZW for float32 data).
 - **Tests**: Run only inside Docker via `./run.sh --test`. Synthetic DEM fixture in `tests/conftest.py`.