Refactor depth surface handling and unify depth sampling rules

- Removed the `always_vertex` parameter from `build_surface_camera` to streamline depth sampling for cutouts and ensure consistent behavior across depth plane and panorama.
- Updated depth sampling logic to ensure that all free boundary points, including the original frame of the depth plane, use neighboring face depth instead of their own texture sampling.
- Adjusted the depth mask deletion process to operate on faces rather than points, eliminating the need for additional cleanup of dangling edges.
- Ensured that the cutout rules are consistently applied across all relevant nodes, removing exceptions and simplifying the logic.
- Updated tests to verify the new behavior, ensuring that cutout points follow the depth of adjacent faces and that the original frame maintains its depth sampling.
- Refactored geometry handling in multiple depth-related nodes to improve clarity and maintainability.

tests/tools/nodes/test_depth_cutout.py

@@ -215,7 +215,8 @@ def test_depth_cutout_reuses_boundary_and_slow_field_nodes():
     group = build_image_depth_cutout_group()
     counts = Counter(node.bl_idname for node in group.nodes)
     assert counts["GeometryNodeInputMeshEdgeNeighbors"] <= 15
-    assert counts["GeometryNodeBlurAttribute"] <= 12
+    # 内部平滑、边界条带与 pin sharp 的法线相干度各一个 Blur。
+    assert counts["GeometryNodeBlurAttribute"] <= 13
 
 
 def test_center_derives_from_shared_slow_fields():