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/res/drawable/status_indicator.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<shape xmlns:android="http://schemas.android.com/apk/res/android"
+    android:shape="oval">
+    <solid android:color="@color/status_stopped" />
+</shape>