refactor(android): split session JNI into modules, HUD-gated stats, AAudio open retry

- native: the 756-line session.rs becomes session/{mod,connect,input,planes}.rs
  around a SessionHandle (connect lifecycle + trust, input plane shims, plane
  start/stop + stats drain).
- Decode-stats sampling is HUD-gated (nativeSetVideoStatsEnabled): with the
  overlay hidden the decode thread skips the per-AU clock read + lock; enabling
  resets the measurement window.
- audio: the AAudio open path is a per-sharing-mode try_open closure — the
  realtime callback state (ring, prime, free-list) is rebuilt per attempt, so a
  failed exclusive-mode try can't leak state into the shared-mode retry.
- Kotlin: ConnectScreen/StreamScreen slimmed by extracting ConnectDialogs,
  StatsOverlay and TouchInput.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/android/native/Cargo.toml

@@ -27,8 +27,8 @@ log = "0.4"
 mdns-sd = "0.20"
 
 # Android-only deps. Gated so `cargo build --workspace` on the Linux/macOS dev boxes + CI still
-# compiles this crate (as a host cdylib) — the Android-framework glue (logging now; AMediaCodec via
-# `ndk` and Oboe/Opus audio later) is only pulled in for the real `*-linux-android` targets.
+# compiles this crate (as a host cdylib) — the Android-framework glue (logging, AMediaCodec + AAudio
+# via `ndk`, the Opus codec) is only pulled in for the real `*-linux-android` targets.
 [target.'cfg(target_os = "android")'.dependencies]
 android_logger = "0.14"
 # NDK bindings. "media" = AMediaCodec/ANativeWindow (video); "audio" = AAudio (audio playback).