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>

Cargo.lock

@@ -46,6 +46,23 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "android_log-sys"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "84521a3cf562bc62942e294181d9eef17eb38ceb8c68677bc49f144e4c3d4f8d"
+
+[[package]]
+name = "android_logger"
+version = "0.14.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "05b07e8e73d720a1f2e4b6014766e6039fd2e96a4fa44e2a78d0e1fa2ff49826"
+dependencies = [
+ "android_log-sys",
+ "env_filter",
+ "log",
+]
+
 [[package]]
 name = "anes"
 version = "0.1.6"
@@ -917,6 +934,16 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "env_filter"
+version = "0.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1bf3c259d255ca70051b30e2e95b5446cdb8949ac4cd22c0d7fd634d89f568e2"
+dependencies = [
+ "log",
+ "regex",
+]
+
 [[package]]
 name = "equivalent"
 version = "1.0.2"
@@ -2411,6 +2438,16 @@ dependencies = [
  "unarray",
 ]
 
+[[package]]
+name = "punktfunk-android"
+version = "0.0.1"
+dependencies = [
+ "android_logger",
+ "jni",
+ "log",
+ "punktfunk-core",
+]
+
 [[package]]
 name = "punktfunk-client-linux"
 version = "0.0.1"
@@ -2715,6 +2752,7 @@ checksum = "75e669e5202259b5314d1ea5397316ad400819437857b90861765f24c4cf80a2"
 dependencies = [
  "aws-lc-rs",
  "pem",
+ "ring",
  "rustls-pki-types",
  "time",
  "yasna",