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/server-cache-display/spec.md

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+# server-cache-display Specification
+
+## Purpose
+TBD - created by archiving change show-server-controls-while-running. Update Purpose after archive.
+## Requirements
+### Requirement: Cached model list layout
+Server 面板 SHALL 显示所有 Cached 模型名称，并 SHALL 在存在多个模型时让每个模型名称占据独立的视觉行。
+
+#### Scenario: Multiple models are cached
+- **WHEN** Server 为 Running 且 Cached 列表包含两个或更多模型
+- **THEN** 面板逐行显示每个模型名称，并保留缓存清理按钮
+
+#### Scenario: One model is cached
+- **WHEN** Server 为 Running 且 Cached 列表只包含一个模型
+- **THEN** 面板在一行内显示 `Cached` 与该模型名称，并保留缓存清理按钮
+
+#### Scenario: No model is cached
+- **WHEN** Server 为 Running 且 Cached 列表为空
+- **THEN** 面板显示 `Cached: None`，并保留缓存清理按钮
+