refactor(android): split C++ into wzp-native cdylib, loaded at runtime

Phase 1 of the big refactor. Escape the Tauri Android
__init_tcb+4 symbol leak (rust-lang/rust#104707) by making
wzp-desktop's Android .so pure Rust — ZERO cc::Build, no cpp/ files,
no C++ in the rustc link step. All future C++ (Oboe audio bridge)
lives in a new standalone cdylib crate `wzp-native` which is built
with cargo-ndk (the same path the legacy wzp-android crate uses
successfully on the same phone + same NDK), copied into Tauri's
gen/android/app/src/main/jniLibs at build time, and dlopened by
wzp-desktop at runtime via libloading.

Changes in this commit:
- NEW crate crates/wzp-native/ with crate-type = ["cdylib"] only
  (no staticlib, no rlib — rust#104707 shows mixing staticlib with
  cdylib leaks non-exported symbols, which is the original bug
  source). Phase 1 scaffold has TWO extern "C" functions:
    wzp_native_version() -> i32            (returns 42)
    wzp_native_hello(buf, cap) -> usize    (writes a string)
  So we can verify dlopen + dlsym + cross-.so FFI end-to-end
  before adding any real C++.
- desktop/src-tauri/cpp/ directory DELETED (7 files gone).
- desktop/src-tauri/build.rs reduced to just the git hash capture
  + tauri_build::build(). No more cc::Build of any kind.
- desktop/src-tauri/Cargo.toml: drop cc from build-dependencies,
  add libloading = "0.8" as an Android-only runtime dep.
- desktop/src-tauri/src/lib.rs Builder::setup() now (on Android only)
  dlopens libwzp_native.so, calls wzp_native_version() and
  wzp_native_hello(), and logs the result:
    "wzp-native dlopen OK: version=42 msg=\"hello from wzp-native\""
  If this log appears in logcat when the app launches and the home
  screen still renders, the split-cdylib pipeline is validated and
  Phase 2 (port the Oboe bridge into wzp-native) can proceed.
- scripts/build-tauri-android.sh: insert a `cargo ndk -t arm64-v8a
  build --release -p wzp-native` step before `cargo tauri android
  build`, with `-o desktop/src-tauri/gen/android/app/src/main/jniLibs`
  so the resulting libwzp_native.so lands in the place gradle will
  package into the final APK.
- Workspace Cargo.toml: add crates/wzp-native to [workspace] members.

Phase 2 (separate commit, only if Phase 1 works):
- Copy cpp/oboe_bridge.{h,cpp} + getauxval_fix.c from the legacy
  wzp-android crate into crates/wzp-native/cpp/.
- Add cc = "1" as a build-dependency on wzp-native (safe: it's a
  single-cdylib crate with no staticlib, so no symbol leak).
- Add build.rs that compiles the Oboe C++ and the wzp-native Rust
  FFI exposes the audio start/stop/read/write functions.
- wzp-desktop::engine.rs dlopens wzp-native at CallEngine::start,
  uses its audio functions instead of CPAL on Android.

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

desktop/src-tauri/src/lib.rs

@@ -535,6 +535,45 @@ pub fn run() {
             }
             tracing::info!("app data dir: {data_dir:?}");
             let _ = APP_DATA_DIR.set(data_dir);
+
+            // Phase 1 smoke test of the separate-cdylib approach to the
+            // __init_tcb crash (see docs/incident-tauri-android-init-tcb.md):
+            // dlopen the sibling libwzp_native.so that gradle dropped into
+            // our jniLibs directory and call its exported wzp_native_version()
+            // + wzp_native_hello() functions. If this logs
+            //   "wzp-native dlopen OK: version=42 msg=...",
+            // we've validated the whole cdylib-split pipeline and can move
+            // to Phase 2 (port the Oboe bridge into wzp-native).
+            #[cfg(target_os = "android")]
+            {
+                match unsafe { libloading::Library::new("libwzp_native.so") } {
+                    Ok(lib) => {
+                        unsafe {
+                            match lib.get::<unsafe extern "C" fn() -> i32>(b"wzp_native_version") {
+                                Ok(version_fn) => {
+                                    let v = version_fn();
+                                    let mut buf = [0u8; 64];
+                                    let msg = match lib.get::<unsafe extern "C" fn(*mut u8, usize) -> usize>(b"wzp_native_hello") {
+                                        Ok(hello_fn) => {
+                                            let n = hello_fn(buf.as_mut_ptr(), buf.len());
+                                            String::from_utf8_lossy(&buf[..n]).into_owned()
+                                        }
+                                        Err(e) => format!("<no hello: {e}>"),
+                                    };
+                                    tracing::info!("wzp-native dlopen OK: version={v} msg=\"{msg}\"");
+                                }
+                                Err(e) => {
+                                    tracing::warn!("wzp-native loaded but dlsym(wzp_native_version) failed: {e}");
+                                }
+                            }
+                        }
+                    }
+                    Err(e) => {
+                        tracing::warn!("wzp-native dlopen failed: {e}");
+                    }
+                }
+            }
+
             Ok(())
         })
         .invoke_handler(tauri::generate_handler![