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/tests/test_cli.py

@@ -85,4 +85,21 @@ class TestSetupLogging:
         assert logger.level == logging.DEBUG
         fmt = logger.handlers[0].formatter._fmt
         assert "%(filename)s" in fmt
-        assert "%(lineno)d" in fmt
+        assert "%(lineno)d" in fmt
+
+
+def test_rebuild_index_without_input_arg(tmp_path):
+    """--rebuild-index fonctionne sans l'argument positionnel input.
+
+    Régression : input était obligatoire alors que --rebuild-index ne
+    l'utilise pas (erreur argparse « the following arguments are required »).
+    """
+    import subprocess
+
+    r = subprocess.run(
+        [sys.executable, "-m", "lidar_pipeline", "--rebuild-index",
+         "-o", str(tmp_path)],
+        capture_output=True, text=True, timeout=180,
+    )
+    assert r.returncode == 0, r.stderr
+    assert "the following arguments are required" not in r.stderr