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/cutout-mesh-sampling/spec.md

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+# cutout-mesh-sampling Specification
+
+## Purpose
+TBD - created by archiving change fix-cutout-density-and-image-edit-names. Update Purpose after archive.
+## Requirements
+### Requirement: Mesh Detail preserves source-pixel spacing
+系统 SHALL 将 Cutout 的 Low、Medium、High、Ultra 分别解释为相邻网格采样点之间 32、16、8、4 个源图像素，并在未触及网格上限时保持该间距。
+
+#### Scenario: Low samples every 32 source pixels
+- **WHEN** 用户以 Low 创建一个未触及网格上限的 Cutout
+- **THEN** 系统按每 32 个源图像素一次的间距构建网格
+
+#### Scenario: Upscale increases linear mesh density
+- **WHEN** 同一图片内容在线性宽高各 Upscale 4 倍后，以相同 Mesh Detail、相同相对 Selection 和相同显示尺寸创建 Cutout，且两次均未触及网格上限
+- **THEN** Upscale 结果在同一线性内容范围内获得约 4 倍网格采样密度
+
+### Requirement: Cutout mesh limit caps actual sampling resolution
+系统 SHALL 仅在 Cutout 实际几何范围的预期采样长边超过 **Maximum Cutout Mesh Resolution** 时增大采样间距，并 SHALL NOT 按 Selection bounds 的原始像素长边直接缩放已经由 Mesh Detail 得到的密度。
+
+#### Scenario: Large pixel bounds remain below the sampling limit
+- **WHEN** Selection bounds 的像素长边超过配置值，但按当前 Mesh Detail 计算的实际采样长边没有超过配置值
+- **THEN** 系统保持该 Mesh Detail 对应的源像素采样间距
+
+#### Scenario: Actual sampling reaches the configured limit
+- **WHEN** Cutout 实际几何范围按当前 Mesh Detail 计算的采样长边超过配置值
+- **THEN** 系统等比增大网格采样间距，使实际采样长边不超过配置值
+