Add specifications for two-times upscale and unified depth plane features

- Introduced the two-times upscale specification detailing requirements for unified output, fixed model presets, arbitrary dimensions, and consistent job behavior.
- Added scenarios for existing models, repeated upscale, and handling of alpha preservation.
- Created the unified depth plane specification outlining geometry modes, stable interface, and asset evaluation.
- Defined scenarios for mode switching, relief and camera preservation, and validation of delivered assets.

openspec/changes/archive/2026-09-17-weight-cutout-boundary-smoothing/tasks.md

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+## 1. Boundary behavior
+
+- [x] 1.1 区分 Depth Cutout 的 Split 与 Outline influence，并在单一平滑循环中应用完整与 0.1 倍权重。
+- [x] 1.2 将 O Image Depth Cutout 的 Boundary Smooth 默认值改为 4，保持零值旁路和既有范围。
+
+## 2. Verification and asset
+
+- [x] 2.1 更新相关行为与接口测试，覆盖 Split 优先、Outline 弱权重、默认值和关闭行为。
+- [x] 2.2 运行相关测试，执行 `uv run node-group build` 并确认保存资产验证通过。