Add segmentation post-processing: dark water fix + wetland reclassify

Two heuristic rules applied after SegEarth-OV3 inference:

1. Dark water: if background pixels have mean_rgb < 0.24 and std < 0.08,
   reclassify as water. Fixes GTA-UAV satellite dark ocean (57% → ~15% bg).

2. Wetland reclassify (GTA-UAV only): split false-positive wetland pixels
   by color — green-dominant → vegetation, else → bare soil. Fixes 14.3%
   muddy/wetland false positives on GTA-V hillside terrain.

Config flags: seg_fix_dark_water (default True), seg_reclassify_wetland
(default False, enabled in run_gta_uav.py).

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

scripts/run_gta_uav.py

@@ -63,6 +63,8 @@ def main() -> None:
         save_vis=True,
         save_safetensors=True,
         cleanup_npy=True,
+        seg_fix_dark_water=True,
+        seg_reclassify_wetland=True,
         resume=True,
         source=source,
         log_level="INFO",