feat(android): live stats HUD + low-latency decode tuning

Stats HUD (mirrors the Apple client): the decode thread accumulates FPS, receive
throughput, and capture->client latency (p50/p95, skew-corrected) in Rust
(clients/android/native/src/stats.rs); nativeVideoStats drains a snapshot ~1 Hz
over JNI as a DoubleArray. StreamScreen renders a Compose overlay
(W*H@Hz / fps / Mb/s / latency, + dropped-under-loss), toggled by a Settings
switch (persisted, default on) or a 3-finger tap.

Performance (decode.rs):
- ANativeWindow_setFrameRate(refresh_hz): align display vsync to the stream rate
  (no 60-in-120 judder); safe since minSdk 31 >= API 30.
- Raise the decode thread toward URGENT_DISPLAY (best-effort setpriority) so
  background work can't preempt it under load.
- Codec low-latency hints KEY_PRIORITY=0 (realtime) + KEY_OPERATING_RATE.

Verified host-side: cargo build/clippy/fmt --workspace (the ungated stats + JNI
accessor). The android-gated decode.rs (NDK) and the Kotlin build only in CI
(android.yml: gradle + cargo-ndk) -- APIs verified against crate sources.

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

clients/android/native/Cargo.toml

@@ -29,6 +29,8 @@ android_logger = "0.14"
 # Pure-Rust FFI to libmediandk/libnativewindow/libaaudio — no C++/libc++_shared to bundle. Decode +
 # audio run entirely in Rust on native threads (the "no async on the hot path" invariant).
 ndk = { version = "0.9", features = ["media", "audio"] }
+# setpriority/gettid to raise the decode thread toward URGENT_DISPLAY (see decode::boost_thread_priority).
+libc = "0.2"
 # Opus decode for the host→client audio plane (0xC9: 48 kHz stereo, 5 ms frames). Same crate the
 # host + Linux client use. audiopus_sys vendors libopus (pure C) and builds it static via cmake —
 # the cargo-ndk build sets LIBOPUS_STATIC=1/LIBOPUS_NO_PKG=1 so it links the bundled lib, not the host's.