Initial commit: Android Tether API app

Exposes phone connection status via HTTP API for tethered devices.

Features:
- Auto-start/stop server when tethering is enabled/disabled
- REST API with /status and /health endpoints
- Connection type, signal strength, carrier, battery info
- Foreground service with persistent notification

Stack: Kotlin 2.3, AGP 8.13, Gradle 8.13, compileSdk 36

app/src/main/java/dev/itsh/tetherapi/receiver/TetherStateReceiver.kt

@@ -0,0 +1,61 @@
+package dev.itsh.tetherapi.receiver
+
+import android.content.BroadcastReceiver
+import android.content.Context
+import android.content.Intent
+import android.net.ConnectivityManager
+import android.os.Build
+import androidx.preference.PreferenceManager
+import dev.itsh.tetherapi.service.TetherApiService
+
+class TetherStateReceiver : BroadcastReceiver() {
+
+    override fun onReceive(context: Context, intent: Intent) {
+        if (intent.action != ACTION_TETHER_STATE_CHANGED) return
+
+        val prefs = PreferenceManager.getDefaultSharedPreferences(context)
+        val autoStartEnabled = prefs.getBoolean(PREF_AUTO_START, true)
+
+        if (!autoStartEnabled) return
+
+        val isTethering = isTetherActive(context, intent)
+        val port = prefs.getInt(PREF_PORT, TetherApiService.DEFAULT_PORT)
+
+        if (isTethering && !TetherApiService.isRunning) {
+            TetherApiService.start(context, port)
+        } else if (!isTethering && TetherApiService.isRunning) {
+            TetherApiService.stop(context)
+        }
+    }
+
+    @Suppress("DEPRECATION")
+    private fun isTetherActive(context: Context, intent: Intent): Boolean {
+        val extras = intent.extras ?: return false
+
+        val activeList = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
+            extras.getStringArrayList("activeArray")
+        } else {
+            @Suppress("UNCHECKED_CAST")
+            extras.get("activeArray") as? ArrayList<String>
+        }
+
+        if (!activeList.isNullOrEmpty()) {
+            return true
+        }
+
+        return try {
+            val cm = context.getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager
+            val method = cm.javaClass.getDeclaredMethod("getTetheredIfaces")
+            val tetheredIfaces = method.invoke(cm) as? Array<*>
+            tetheredIfaces != null && tetheredIfaces.isNotEmpty()
+        } catch (e: Exception) {
+            false
+        }
+    }
+
+    companion object {
+        const val ACTION_TETHER_STATE_CHANGED = "android.net.conn.TETHER_STATE_CHANGED"
+        const val PREF_AUTO_START = "auto_start_on_tether"
+        const val PREF_PORT = "api_port"
+    }
+}