Lower segmentation threshold to 0.1 for UAV_VisLoc

Default 0.3 was too aggressive — dark water, muddy ground, and
uniform textures fell below confidence threshold. Lower to 0.1
to reduce false background pixels.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/run_uav_visloc.py

@@ -73,7 +73,7 @@ def main() -> None:
     )
 
     input_conf = InputConfig(image_size=256)
-    seg_conf = SegConfig(prompts=[
+    seg_conf = SegConfig(threshold=0.1, prompts=[
         "background",                   # 0
         "building",                     # 1
         "road",                         # 2