Add comprehensive documentation for SnapForm features and workflows

- Introduced new guides for Depth Plane, Surface, and animation workflows.
- Added installation instructions and FAQs to assist users in setup and troubleshooting.
- Created a quick-start guide for first-time users to convert images to Depth Planes.
- Documented the process for removing backgrounds from images.
- Established a models and storage section to clarify data management.
- Included a stylesheets file for improved documentation styling.
- Updated mkdocs configuration for better navigation and theme settings.

docs/depth-plane.md

@@ -1,5 +1,8 @@
 # Depth Plane
 
+本页记录 Depth Plane 的数据、节点和材质实现。日常操作与参数说明请阅读
+[Depth Plane 使用指南](guide-depth-plane.md)。
+
 ## Image Empty 转深度面片
 
 1. 在 3D View 选中 `Object Type = Empty`、`Display As = Image` 的对象。