Reorganized repository into backend and frontend directories

.gitignore

@@ -1,12 +1,52 @@
-# 编译产物
+# --- Root ---
-/server
+.DS_Store
-*.exe
-*.out
-
-# 依赖库
-/vendor/
-
-# 编辑器与系统生成
 .idea/
 .vscode/
-.DS_Store
+
+# --- Backend (Go) ---
+backend/hightube.db
+backend/server
+backend/*.exe
+backend/*.out
+backend/vendor/
+
+# --- Frontend (Flutter) ---
+frontend/.dart_tool/
+frontend/.packages
+frontend/.pub-cache/
+frontend/.pub/
+frontend/build/
+frontend/ios/Flutter/Generated.xcconfig
+frontend/ios/Flutter/flutter_export_environment.sh
+frontend/android/local.properties
+frontend/android/app/src/main/res/drawable/launch_background.xml
+frontend/android/app/src/main/res/values/styles.xml
+frontend/android/app/src/main/res/values-night/styles.xml
+frontend/android/app/src/main/res/mipmap-mdpi/ic_launcher.png
+frontend/android/app/src/main/res/mipmap-hdpi/ic_launcher.png
+frontend/android/app/src/main/res/mipmap-xhdpi/ic_launcher.png
+frontend/android/app/src/main/res/mipmap-xxhdpi/ic_launcher.png
+frontend/android/app/src/main/res/mipmap-xxxhdpi/ic_launcher.png
+frontend/android/app/src/main/res/values-v21/styles.xml
+frontend/android/app/src/main/res/values-v21/styles-night.xml
+frontend/android/app/src/main/res/values-v11/styles.xml
+frontend/android/app/src/main/res/values-v11/styles-night.xml
+frontend/ios/Runner/Assets.xcassets/AppIcon.appiconset/*.png
+frontend/ios/Runner/Base.lproj/LaunchScreen.storyboard
+frontend/ios/Runner/Base.lproj/Main.storyboard
+frontend/ios/Runner/Info.plist
+frontend/ios/Runner/Runner.entitlements
+frontend/linux/flutter/generated_plugins.cmake
+frontend/macos/Flutter/Generated.xcconfig
+frontend/macos/Flutter/ephemeral/
+frontend/windows/flutter/generated_plugins.cmake
+frontend/windows/flutter/generated_plugin_registrant.cc
+frontend/windows/flutter/generated_plugin_registrant.h
+frontend/web/index.html
+frontend/web/favicon.png
+frontend/web/manifest.json
+frontend/web/robots.txt
+frontend/web/icons/Icon-192.png
+frontend/web/icons/Icon-512.png
+frontend/web/icons/Icon-maskable-192.png
+frontend/web/icons/Icon-maskable-512.png