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/features.md

@@ -1,7 +1,7 @@
-# 功能与使用
+# 功能参考
 
-本文档面向开发者和需要了解内部实现细节的用户，从原 README 迁移而来。普通用户请阅读项目根目录的
-`README.md`。
+本页记录完整功能行为和实现边界，主要供开发、测试与故障排查使用。第一次使用 SnapForm 时，请从
+[安装与首次配置](installation.md)或[五分钟上手](quick-start.md)开始。
 
 `SnapForm` 是一套从图片快速构建空间结构的 Blender Extension。目前以
 [Depth Anything 3](https://github.com/ByteDance-Seed/Depth-Anything-3)