Add comprehensive documentation for SnapForm extension

- Created development.md for development setup and licensing information.
- Added features.md detailing functionalities and usage instructions for developers and users.
- Introduced index.md to serve as a navigation hub for the documentation.
- Developed outputs.md to explain output formats and their specifications.
- Established service.md to describe the AI Service architecture and environment setup.
- Created surface.md to outline the process of converting Image Empty to perspective meshes.

docs/outputs.md

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+# 输出格式
+
+## 输出格式说明
+
+`Output Type` 提供以下结果：
+
+- Point Cloud (GLB)：DA3 `glb`
+- Gaussian Splats (PLY)：DA3 `gs_ply`，同时传入 `infer_gs=True`
+- Depth Preview (Images)：DA3 `depth_vis`
+- Depth Data (NPZ)：DA3 `mini_npz`
+- Textured Surface (GLB)：SnapForm 根据 DA3 Prediction 构建并输出 `mesh.glb`
+
+Point Cloud 专属设置仅在对应类型下显示，`gs_views_interval` 仅用于 Gaussian Splats。
+Textured Surface 使用 0–100% 的 Confidence Threshold 删除置信度最低的一定比例：
+
+- `process_res=504`
+- `process_res_method="upper_bound_resize"`
+- `use_ray_pose=False`
+- `ref_view_strategy="saddle_balanced"`
+- `conf_thresh_percentile=40.0`
+- `num_max_points=1_000_000`
+- `show_cameras=True`
+- `export_kwargs["gs_ply"]["gs_views_interval"]=1`
+
+DA3 官方 `glb` 是彩色点云与可选相机线框；`gs_ply` 是带 Gaussian 属性的 PLY；
+`depth_vis` 是原图与着色深度图的并排预览；`mini_npz` 保存深度、置信度和可用的相机参数。
+Point Cloud GLB 任务会关闭其默认附带的深度预览，使五种输出产物保持分离。
+
+官方格式与限制可参阅
+[DA3 Python API 文档](https://github.com/ByteDance-Seed/Depth-Anything-3/blob/main/docs/API.md)。
+