Add web map with zone generation API, side job queue, and restore historical DTM hole rendering

- webapp.py: FastAPI serving the continuous map (port 8973) with
  /api/preview, /api/generate and /api/status; tiles are downloaded
  from IGN and processed in a logged subprocess, tracked live in a
  side "File de génération" panel that survives page reloads
- fetch_ign.py: download missing 1 km LiDAR HD tiles from the IGN
  geoplateforme before processing
- index.py: tile thumbnails and 500 m subtiles are now invalidated by
  mtime so regenerating a tile refreshes its cached images; progress
  logging per tile
- dtm.py: back to the historical gap handling (small gaps filled by
  fillnodata only, larger holes left as nodata rendered black);
  lowest-return floor only via --bare-earth, IGN class selection via
  --ign-classes
- cli.py: positional input now optional (--rebuild-index works alone)
- docker-compose.yml: serve (GPU, port 8973) and process services;
  launch via docker compose only (documented in AGENTS.md/AGENTS.md)
- tests: 131 passing, incl. regressions for thumbnail staleness,
  --rebuild-index without input, and nodata rendering

lidar_pipeline/rendering.py

@@ -818,8 +818,11 @@ def tif_to_crop(tif_file, vis_dir, resolution, keep_tif=False, quality=98, outpu
 
         # Convert to RGB using colormap
         if is_rgb_result:
-            # RGB images are already in RGB
-            rgb_data = (data * 255).astype(np.uint8)
+            # RGB images are already in RGB (uint8 depuis le TIF IGN, ou float 0-1)
+            if data.dtype == np.uint8:
+                rgb_data = data
+            else:
+                rgb_data = (np.clip(data, 0, 1) * 255).astype(np.uint8)
         else:
             # Normalize data to 0-1 range for colormap
             cmap = plt.get_cmap(cmap_name)