fix: Android signal thread stack overflow + add version marker to UI

- Spawn signaling on dedicated thread with 4MB stack instead of using
  Android's IO dispatcher thread (insufficient stack for tokio + QUIC)
- Add "direct-call-v1" version marker to home screen subtitle

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

Cargo.lock

@@ -4370,6 +4370,7 @@ dependencies = [
  "async-trait",
  "axum 0.7.9",
  "bytes",
+ "chrono",
  "dirs",
  "futures-util",
  "prometheus",

android/app/src/main/java/com/wzp/ui/call/InCallScreen.kt

@@ -165,7 +165,7 @@ fun InCallScreen(
                     color = Color.White
                 )
                 Text(
-                    text = "ENCRYPTED VOICE",
+                    text = "ENCRYPTED VOICE  \u2022  direct-call-v1",
                     style = MaterialTheme.typography.labelSmall.copy(letterSpacing = 3.sp),
                     color = TextDim
                 )

crates/wzp-android/src/engine.rs

@@ -272,14 +272,19 @@ impl WzpEngine {
 
         info!(fingerprint = %fp, relay = %addr, "starting signaling");
 
-        // Create runtime for signaling (separate from call runtime)
+        self.state.running.store(true, Ordering::Release);
-        let rt = tokio::runtime::Builder::new_multi_thread()
-            .worker_threads(1)
-            .enable_all()
-            .build()?;
-
         let signal_state = state.clone();
-        rt.spawn(async move {
+
+        // Spawn on a dedicated thread with sufficient stack (Android IO dispatcher stack is too small)
+        std::thread::Builder::new()
+            .name("wzp-signal".into())
+            .stack_size(4 * 1024 * 1024) // 4MB stack
+            .spawn(move || {
+                let rt = tokio::runtime::Builder::new_current_thread()
+                    .enable_all()
+                    .build()
+                    .expect("tokio runtime");
+                rt.block_on(async move {
             let _ = rustls::crypto::ring::default_provider().install_default();
             let bind: SocketAddr = "0.0.0.0:0".parse().unwrap();
             let endpoint = match wzp_transport::create_endpoint(bind, None) {
@@ -371,9 +376,9 @@ impl WzpEngine {
 
             let mut stats = signal_state.stats.lock().unwrap();
             stats.state = crate::stats::CallState::Closed;
-        });
+                }); // block_on
+            })?; // thread spawn
 
-        self.tokio_runtime = Some(rt);
         Ok(())
     }