feat(android): scaffold the native Android client (Rust-heavy JNI bridge)

Rust-heavy client model (like punktfunk-client-linux): a new cdylib crate
crates/punktfunk-android links punktfunk-core and exposes the JNI seam;
Kotlin (clients/android) owns only the Android-framework surface. Kotlin can't
import the C header the way Swift can, so the bridge is written in Rust to reuse
the Linux client's orchestration rather than re-port it.

- crates/punktfunk-android: JNI bridge — abiVersion/coreVersion native-link
  proof + session connect/close handle; plane pumps stubbed for M4 stage 1.
- clients/android: Gradle project — :app (Compose) + :kit (Android library with
  a cargo-ndk Exec task -> jniLibs). AGP 9.2 / Gradle 9.4.1 / Kotlin 2.3.21 /
  Compose BOM 2026.05.01 / compileSdk 37 / targetSdk 36 / minSdk 31, shipping
  arm64-v8a + x86_64. Phone + TV (leanback) installable. README rewritten.
- .gitea/workflows/android.yml: CI mirroring apple.yml on a Linux runner.
- punktfunk-core: switch rcgen to the ring backend so the whole quic tree is
  aws-lc-free (smaller client .so, cmake-free cross-compile; a win for all targets).

Validated on this box: :app:assembleDebug -> APK with both ABIs; emulator
first-light renders the bridge linked (core ABI v2) with logcat confirmation;
clippy -D warnings + cargo fmt clean; core tests green on the ring backend.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/android/app/src/main/AndroidManifest.xml

@@ -0,0 +1,45 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <!-- punktfunk/1 QUIC/UDP data plane. -->
+    <uses-permission android:name="android.permission.INTERNET" />
+    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
+    <!-- mDNS discovery of _punktfunk._udp on the LAN (NsdManager). -->
+    <uses-permission
+        android:name="android.permission.NEARBY_WIFI_DEVICES"
+        android:usesPermissionFlags="neverForLocation" />
+    <!-- Enforced from Android 17 (SDK 37) for ALL local-network traffic incl. the QUIC socket.
+         Harmless to declare on earlier releases. -->
+    <uses-permission android:name="android.permission.ACCESS_LOCAL_NETWORK" />
+    <!-- Mic uplink to the host's virtual microphone (requested at runtime). -->
+    <uses-permission android:name="android.permission.RECORD_AUDIO" />
+    <!-- Gamepad rumble feedback. -->
+    <uses-permission android:name="android.permission.VIBRATE" />
+
+    <!-- We target phone + TV from day one: keep the app installable on TV (no touchscreen) and on
+         devices without a gamepad. -->
+    <uses-feature android:name="android.hardware.touchscreen" android:required="false" />
+    <uses-feature android:name="android.software.leanback" android:required="false" />
+    <uses-feature android:name="android.hardware.gamepad" android:required="false" />
+
+    <application
+        android:allowBackup="true"
+        android:icon="@android:drawable/sym_def_app_icon"
+        android:label="@string/app_name"
+        android:supportsRtl="true"
+        android:theme="@style/Theme.PunktfunkAndroid">
+
+        <activity
+            android:name=".MainActivity"
+            android:exported="true"
+            android:configChanges="orientation|screenSize|keyboardHidden|screenLayout|density|navigation"
+            android:theme="@style/Theme.PunktfunkAndroid">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+                <!-- TV launcher entry. -->
+                <category android:name="android.intent.category.LEANBACK_LAUNCHER" />
+            </intent-filter>
+        </activity>
+    </application>
+</manifest>