rename io_classifier → scene_classifier

The "IO" name was a Places365 carry-over (their IO_places365.txt label
file marks each category as Indoor/Outdoor). In Python "IO" reads as
input/output by default and obscures what the module actually does.
``scene_classifier`` matches the existing ``--scene_mode`` flag and
the ``_resolve_scene`` helper in app.py. The internal references to the
upstream IO_places365.txt resource are kept intact.

app.py

@@ -46,7 +46,7 @@ from src.utils.geometry_utils import (
     erp_to_pointcloud,
     remove_isolated_clusters_3d,
 )
-from src.utils.io_classifier import get_classifier
+from src.utils.scene_classifier import get_classifier
 from src.utils.utils import (
     prepare_depth_for_logging,
     prepare_normals_for_logging,
@@ -109,7 +109,7 @@ def _resolve_scene(mode: str, input_rgb: np.ndarray) -> tuple[str, str]:
     classifier to pick a head; otherwise echoes the explicit choice."""
     if mode in (MODE_INDOOR, MODE_OUTDOOR):
         return mode, f"**Scale head:** {mode}"
-    label, _ = io_classifier.classify(input_rgb)
+    label, _ = scene_classifier.classify(input_rgb)
     scene = MODE_OUTDOOR if label == "outdoor" else MODE_INDOOR
     return scene, f"**Scale head:** Auto → {scene}"
 
@@ -369,7 +369,7 @@ pager.model.eval()
 
 # Eager-init the classifier so the first ``Auto`` click doesn't pay the (~1 s)
 # weight load + the (~10 s on first run) download.
-io_classifier = get_classifier(device=device)
+scene_classifier = get_classifier(device=device)
 
 
 _CUSTOM_CSS = """

src/utils/{io_classifier.py → scene_classifier.py}

@@ -117,7 +117,7 @@ class IndoorOutdoorClassifier:
         io_path = cache_dir / "IO_places365.txt"
         for url, dst in [(_WEIGHTS_URL, weights_path), (_IO_URL, io_path)]:
             if not dst.exists():
-                print(f"[io_classifier] downloading {url}", file=sys.stderr)
+                print(f"[scene_classifier] downloading {url}", file=sys.stderr)
                 urllib.request.urlretrieve(url, dst)
 
         is_outdoor = []