feat(android): video decode pipeline — NDK AMediaCodec → SurfaceView

M4 Android stage 1 (video). Pull HEVC access units from the connector and render
them to the SurfaceView entirely in Rust (NDK AMediaCodec → ANativeWindow) — no
per-frame JNI, honoring the native-thread hot-path invariant.

- crates/punktfunk-android: decode.rs (one-in/one-out AMediaCodec loop; in-band
  VPS/SPS/PPS so no out-of-band csd; dims from NativeClient::mode). SessionHandle
  now holds an Arc<NativeClient> + the decode thread; nativeStartVideo/nativeStopVideo.
- clients/android: connect screen (host/port) + full-screen SurfaceView stream
  screen — surfaceCreated -> nativeStartVideo, leaving -> stop + close.

Verified live (Android emulator -> m3-host on the LAN box, ABI v2): QUIC handshake,
8-round clock-skew sync, HEVC decoder configured at 1280x720, and the data plane
delivered + fed all 299 access units (the punktfunk/1 NAT hole-punch worked through
the emulator's SLIRP). Real-pixel render is pending a non-synthetic source:
`m3-host --source synthetic` emits dummy transport payloads (not HEVC), so the
decoder correctly produces nothing; `--source virtual` (a compositor on the host)
is needed to verify decode-to-screen.

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

Cargo.lock

@@ -2049,6 +2049,30 @@ dependencies = [
  "windows-sys 0.61.2",
 ]
 
+[[package]]
+name = "ndk"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3f42e7bbe13d351b6bead8286a43aac9534b82bd3cc43e47037f012ebfd62d4"
+dependencies = [
+ "bitflags",
+ "jni-sys 0.3.1",
+ "log",
+ "ndk-sys",
+ "num_enum",
+ "raw-window-handle",
+ "thiserror 1.0.69",
+]
+
+[[package]]
+name = "ndk-sys"
+version = "0.6.0+11769913"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ee6cda3051665f1fb8d9e08fc35c96d5a244fb1be711a03b71118828afc9a873"
+dependencies = [
+ "jni-sys 0.3.1",
+]
+
 [[package]]
 name = "nix"
 version = "0.30.1"
@@ -2161,6 +2185,28 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "num_enum"
+version = "0.7.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5d0bca838442ec211fa11de3a8b0e0e8f3a4522575b5c4c06ed722e005036f26"
+dependencies = [
+ "num_enum_derive",
+ "rustversion",
+]
+
+[[package]]
+name = "num_enum_derive"
+version = "0.7.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "680998035259dcfcafe653688bf2aa6d3e2dc05e98be6ab46afb089dc84f1df8"
+dependencies = [
+ "proc-macro-crate",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "oid-registry"
 version = "0.7.1"
@@ -2445,6 +2491,7 @@ dependencies = [
  "android_logger",
  "jni",
  "log",
+ "ndk",
  "punktfunk-core",
 ]
 
@@ -2724,6 +2771,12 @@ dependencies = [
  "rand_core 0.9.5",
 ]
 
+[[package]]
+name = "raw-window-handle"
+version = "0.6.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "20675572f6f24e9e76ef639bc5552774ed45f1c30e2951e1e99c59888861c539"
+
 [[package]]
 name = "rayon"
 version = "1.12.0"