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/surface.md

@@ -1,5 +1,8 @@
 # Surface
 
+本页记录 Surface 的网格、相机、Geometry Nodes 和材质实现。日常操作与参数说明请阅读
+[Surface 使用指南](guide-surface.md)。
+
 ## Image Empty 转透视网格
 
 1. 在 3D View 选中仅包含一帧的 Image Empty，右键打开 `SnapForm` 子菜单并选择