Refactor depth reference handling and cleanup

- Unified reference depth calculation to use a single implementation in common/depth.py.
- Removed server-side reference depth computation and adjusted depth.json to only include image_size and intrinsics.
- Updated depth texture handling to ignore transparent, invalid, and non-positive pixels when calculating reference depth.
- Changed reference depth calculation to use the 95th percentile of valid depth values.
- Adjusted depth direction fitting to return a flat direction when no samples are available.
- Removed cleanup threshold parameters from Cutout and related nodes, simplifying the interface.
- Updated tests to verify new reference depth logic and ensure compatibility with existing functionality.

tools/nodes/groups/image_relief_plane.py

@@ -42,7 +42,7 @@ def build_image_relief_plane_group(image_plane_group):
     thickness.description = "Set the thickness of the flat base beneath the relief."
     vector_input(group, "Depth Direction", (0, 0, 1), subtype="DIRECTION").description = "Set the direction used to orient the reference depth plane."
     depth_offset = _interface_socket(group, "Depth Offset", "INPUT", "NodeSocketFloat")
-    depth_offset.default_value = 1.0
+    depth_offset.default_value = 0.0
     depth_offset.min_value = -10.0
     depth_offset.max_value = 10.0
     depth_offset.subtype = "DISTANCE"