feat(android): oboe/AAudio audio backend + runtime mic permission (step 3)

This is the big one — the Tauri Android app now has a real audio stack
capable of full-duplex VoIP, reusing the proven C++ Oboe bridge from the
legacy wzp-android crate.

Architecture:
- desktop/src-tauri/cpp/  — copies of oboe_bridge.{h,cpp}, oboe_stub.cpp,
  and getauxval_fix.c from crates/wzp-android/cpp/. build.rs clones
  google/oboe@1.8.1 into OUT_DIR and compiles the bridge + all Oboe
  sources as "oboe_bridge" static lib, linking against shared libc++
  (static would pull broken libc stubs that SIGSEGV in .so libraries).
- src/oboe_audio.rs  — Rust side: an SPSC ring buffer matching the C++
  bridge's AtomicI32 layout, plus OboeHandle::start() which returns
  (capture_ring, playout_ring, owning_handle). The ring exposes the same
  (available / read / write) methods as wzp_client::audio_ring::AudioRing
  so CallEngine treats both backends interchangeably.
- src/engine.rs  — compiled on every platform now. A cfg-switched type
  alias picks wzp_client::audio_ring::AudioRing on desktop and
  crate::oboe_audio::AudioRing on Android. The audio setup block has
  three branches: VPIO/CPAL on macOS, CPAL on Linux/Windows, Oboe on
  Android. Send/recv tasks are identical across platforms.
- src/lib.rs  — removes all the "step 3 not done" Android stubs. The
  engine module is no longer cfg-gated; connect / disconnect / toggle_mic
  / toggle_speaker / get_status are single implementations used by both
  desktop and Android. Identity path resolves via app.path().app_data_dir()
  from the Tauri setup() callback (already wired in step 1).

Runtime mic permission:
- scripts/build-tauri-android.sh now injects RECORD_AUDIO + MODIFY_AUDIO_
  SETTINGS into gen/android/app/src/main/AndroidManifest.xml after init,
  and overwrites MainActivity.kt with a version that calls
  ActivityCompat.requestPermissions in onCreate. This is idempotent:
  every build re-applies the patches so tauri re-init can't regress them.

Cargo.toml:
- cc is now an unconditional build-dep (build.rs runs on the host, so
  target-gating build-deps doesn't work).
- wzp-client is now a dep on every platform. On Android it gets default
  features only (no "audio"/"vpio") so CPAL isn't dragged in — oboe_audio
  provides the capture/playout rings instead.
- tracing-android is added on Android so tracing events flow into logcat.

build.rs also gained embedded git hash (WZP_GIT_HASH) capture, which is
shown under the fingerprint on the home screen — already committed in
7639aaf, reinstated here alongside the Oboe build logic.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/build-tauri-android.sh

@@ -179,6 +179,45 @@ if [ "${DO_INIT}" = "1" ] || [ ! -x gen/android/gradlew ]; then
     cargo tauri android init 2>&1 | tail -20
 fi
 
+# ── Post-init patches: runtime mic permission + jniLibs dir ─────────────────
+MANIFEST=gen/android/app/src/main/AndroidManifest.xml
+if ! grep -q "RECORD_AUDIO" "$MANIFEST"; then
+    echo ">>> injecting RECORD_AUDIO + MODIFY_AUDIO_SETTINGS into AndroidManifest"
+    sed -i "s|<uses-permission android:name=\"android.permission.INTERNET\" />|<uses-permission android:name=\"android.permission.INTERNET\" />\n    <uses-permission android:name=\"android.permission.RECORD_AUDIO\" />\n    <uses-permission android:name=\"android.permission.MODIFY_AUDIO_SETTINGS\" />|" "$MANIFEST"
+fi
+
+# Overwrite MainActivity to request the mic permission on launch. Idempotent —
+# Tauri re-init would reset it, and we re-write it here on every build.
+MAIN_ACTIVITY=gen/android/app/src/main/java/com/wzp/desktop/MainActivity.kt
+cat > "$MAIN_ACTIVITY" <<KOTLIN_EOF
+package com.wzp.desktop
+
+import android.Manifest
+import android.content.pm.PackageManager
+import android.os.Bundle
+import androidx.activity.enableEdgeToEdge
+import androidx.core.app.ActivityCompat
+
+class MainActivity : TauriActivity() {
+  override fun onCreate(savedInstanceState: Bundle?) {
+    enableEdgeToEdge()
+    super.onCreate(savedInstanceState)
+
+    // Auto-request RECORD_AUDIO + MODIFY_AUDIO_SETTINGS on first launch — Oboe
+    // capture fails silently without them.
+    val needed = arrayOf(
+      Manifest.permission.RECORD_AUDIO,
+      Manifest.permission.MODIFY_AUDIO_SETTINGS,
+    ).filter {
+      ActivityCompat.checkSelfPermission(this, it) != PackageManager.PERMISSION_GRANTED
+    }.toTypedArray()
+    if (needed.isNotEmpty()) {
+      ActivityCompat.requestPermissions(this, needed, 1337)
+    }
+  }
+}
+KOTLIN_EOF
+
 echo ">>> cargo tauri android build ${PROFILE_FLAG} --target aarch64 --apk"
 cargo tauri android build ${PROFILE_FLAG} --target aarch64 --apk