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/specs/image-result-materials/spec.md

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+# image-result-materials Specification
+
+## Purpose
+TBD - created by archiving change refine-image-output-semantics. Update Purpose after archive.
+## Requirements
+### Requirement: Image color drives generated material IOR Level
+系统 SHALL 将 Plane、Depth Plane 与 Cutout 的非 Shadeless 生成材质中 `O Image Layer` 的 Color 输出直接连接到 Principled BSDF 的 IOR Level，同时保留既有 IOR、Base Color、Roughness、Alpha、Normal 与 Displacement 连接。
+
+#### Scenario: Dark image content suppresses highlights
+- **WHEN** 生成材质采样到黑色或暗色图片内容
+- **THEN** Principled BSDF 的 IOR Level SHALL 接收对应的低颜色值，从而降低该区域的高亮
+
+#### Scenario: Bright image content preserves direct color response
+- **WHEN** 生成材质采样到白色或亮色图片内容
+- **THEN** Principled BSDF 的 IOR Level SHALL 接收 `O Image Layer` Color 的直接转换值，不经过额外缩放或固定上限
+
+#### Scenario: Generated material keeps its IOR value
+- **WHEN** Cutout 或 Depth Plane 以 IOR `1.2` 创建材质
+- **THEN** 系统 SHALL 保留 IOR `1.2`，并由 Color 独立驱动 IOR Level
+