feat: 添加 USB 摄像头连接功能

- 新增 Android USB 摄像头 APP (MJPEG 服务器)
- 电脑端支持 ADB 端口转发连接
- 修复 .gitignore 忽略 Android 文件

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

android-app/gradle.properties

@@ -0,0 +1,14 @@
+# Project-wide Gradle settings
+org.gradle.jvmargs=-Xmx2048m -Dfile.encoding=UTF-8
+android.useAndroidX=true
+android.enableJetifier=true
+android.defaults.buildfeatures.resvalues=true
+android.sdk.defaultTargetSdkToCompileSdkIfUnset=false
+android.enableAppCompileTimeRClass=false
+android.usesSdkInManifest.disallowed=false
+android.uniquePackageNames=false
+android.dependency.useConstraints=true
+android.r8.strictFullModeForKeepRules=false
+android.r8.optimizedResourceShrinking=false
+android.builtInKotlin=false
+android.newDsl=false