Update README for Kotlin/Gradle migration

- Update build system from Maven to Gradle
- Update prerequisites (JDK 11+, Gradle 8.1+, NDK 25.1, CMake 3.22.1)
- Remove outdated Travis CI badge and nightly builds link
- Update dependency list (remove unused cntlm, transproxy, stunnel; add tun2socks)
- Add project structure documentation
- Add supported architectures section
- Add SDK version requirements

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: 2 people

README.md

@@ -2,44 +2,69 @@
 
 Global Proxy App for Android System
 
-ProxyDroid is distributed under GPLv3 with many other open source software, 
+ProxyDroid is distributed under GPLv3 with many other open source software,
 here is a list of them:
 
- * cntlm - authentication proxy: http://cntlm.sourceforge.net/
  * redsocks - transparent socks redirector: http://darkk.net.ru/redsocks/
+ * tun2socks - VPN-based transparent proxy
  * netfilter/iptables - NAT module: http://www.netfilter.org/
- * transproxy - transparent proxy for HTTP: http://transproxy.sourceforge.net/
- * stunnel - multiplatform SSL tunneling proxy: http://www.stunnel.org/
 
-## TRAVIS CI STATUS
+## PREREQUISITES
 
-[![Build Status](https://secure.travis-ci.org/madeye/proxydroid.png)](http://travis-ci.org/madeye/proxydroid)
+* JDK 11+
+* Android Studio or Gradle 8.1+
+* Android SDK (compileSdk 33)
+* Android NDK 25.1.8937393
+* CMake 3.22.1
 
-[Nightly Builds](http://buildbot.sinaapp.com)
+## BUILD
 
-## PREREQUISITES
+### Using Android Studio
 
-* JDK 1.6+
-* Maven 3.0.5
-* Android SDK r17+
-* Android NDK r8+
+1. Open the project in Android Studio
+2. Sync Gradle files
+3. Build the project using `Build > Make Project`
 
-* Local Maven Dependencies
+### Using Command Line
 
-  Use Maven Android SDK Deployer to install all android related dependencies.
+```bash
+./gradlew assembleDebug
+```
 
-  ```bash
-  git clone https://github.com/mosabua/maven-android-sdk-deployer.git 
-  pushd maven-android-sdk-deployer
-  export ANDROID_HOME=/path/to/android/sdk
-  mvn install -P 4.1
-  popd
-  ```
+For release build:
 
-## BUILD
+```bash
+./gradlew assembleRelease
+```
 
-Invoke the building like this
+## PROJECT STRUCTURE
 
-```bash
-  mvn clean install
 ```
+app/
+├── src/main/
+│   ├── java/org/proxydroid/    # Kotlin source files
+│   │   ├── ProxyDroid.kt       # Main activity
+│   │   ├── ProxyDroidService.kt
+│   │   ├── ProxyDroidVpnService.kt
+│   │   ├── AppManager.kt
+│   │   ├── Profile.kt
+│   │   └── utils/              # Utility classes
+│   └── cpp/                    # Native code
+│       ├── exec/               # Native exec helper
+│       ├── libevent/           # libevent library
+│       ├── redsocks/           # redsocks proxy
+│       └── tun2socks/          # tun2socks VPN helper
+└── build.gradle
+```
+
+## SUPPORTED ARCHITECTURES
+
+* armeabi-v7a
+* arm64-v8a
+* x86
+* x86_64
+
+## REQUIREMENTS
+
+* Minimum SDK: 21 (Android 5.0)
+* Target SDK: 33 (Android 13)