docs: 添加 UE5.7 项目 Git 配置与开发规范

- 优化 .gitignore 为 UE5.7 专用版本（新增 Rider/VSCode/日志/崩溃/系统文件等）
- 添加 .gitattributes 配置二进制资产处理与 Git LFS 追踪
- 添加 docs/GIT-GUIDE.md 分支策略与提交规范文档
- 添加 .claude/settings.json 项目级权限配置

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitattributes

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+# UE5 Git Attributes - ChildHood Project
+
+# ==============================
+# 二进制资产（禁止文本合并，避免损坏）
+# ==============================
+*.uasset binary
+*.umap binary
+
+# ==============================
+# Git LFS 大文件追踪
+# ==============================
+*.uasset filter=lfs diff=lfs merge=lfs -text
+*.umap filter=lfs diff=lfs merge=lfs -text
+
+# ==============================
+# 美术资源
+# ==============================
+*.png filter=lfs diff=lfs merge=lfs -text
+*.jpg filter=lfs diff=lfs merge=lfs -text
+*.jpeg filter=lfs diff=lfs merge=lfs -text
+*.tga filter=lfs diff=lfs merge=lfs -text
+*.bmp filter=lfs diff=lfs merge=lfs -text
+*.psd filter=lfs diff=lfs merge=lfs -text
+*.ai filter=lfs diff=lfs merge=lfs -text
+
+# ==============================
+# 3D 模型
+# ==============================
+*.fbx filter=lfs diff=lfs merge=lfs -text
+*.obj filter=lfs diff=lfs merge=lfs -text
+*.gltf filter=lfs diff=lfs merge=lfs -text
+*.glb filter=lfs diff=lfs merge=lfs -text
+
+# ==============================
+# 音频
+# ==============================
+*.wav filter=lfs diff=lfs merge=lfs -text
+*.mp3 filter=lfs diff=lfs merge=lfs -text
+*.ogg filter=lfs diff=lfs merge=lfs -text
+*.flac filter=lfs diff=lfs merge=lfs -text
+
+# ==============================
+# 视频
+# ==============================
+*.mp4 filter=lfs diff=lfs merge=lfs -text
+*.avi filter=lfs diff=lfs merge=lfs -text
+*.mov filter=lfs diff=lfs merge=lfs -text
+*.wmv filter=lfs diff=lfs merge=lfs -text
+
+# ==============================
+# 文本 / 代码（正常 diff）
+# ==============================
+*.cpp text
+*.h text
+*.cs text
+*.json text
+*.ini text
+*.cfg text
+*.md text
+*.txt text
+*.uproject text
+*.uplugin text
+*.Build.cs text
+*.Target.cs text
+
+# ==============================
+# 自动换行（Windows 开发环境）
+# ==============================
+* text=auto