feat(protocol): A.1 — fix hostname resolution on Android and iOS

Resolves the Beta-blocking issue surfaced during Android v0.2.0-beta.1
verification: hostnames could not be used, only literal IPs.

Root cause:
  tsclientlib's built-in resolver uses hickory-resolver, which reads
  /etc/resolv.conf. That file does not exist on Android or iOS, so
  any connect by hostname exited the connection task before
  signalling ready and surfaced the cryptic error
    BridgeError.connection(field0: protocol backend:
      connection task exited before signalling ready)

Fix:
  crates/chanora_protocol/src/resolver.rs (new):
    Resolves hostnames via tokio::net::lookup_host, which uses the
    platform's getaddrinfo. Works on every platform Chanora targets.
    Tiny in-process positive-result cache (5 min TTL) keeps
    reconnects cheap. IPv4 sorted ahead of IPv6 in the returned list
    to favour the more reliable path on dual-stack networks.

  crates/chanora_protocol/src/adapter.rs:
    connection_task now resolves the hostname itself and passes the
    resulting SocketAddr (not the hostname String) to
    tsclientlib::Connection::build. tsclientlib's ServerAddress enum
    accepts SocketAddr via its From impl, so the upstream resolver
    is skipped entirely.

  crates/chanora_protocol/src/lib.rs:
    New typed error arm ProtocolError::DnsFailed { host, reason }
    so the UI can distinguish 'server not found' from 'server
    refused our packets'.

  crates/chanora_bridge/src/lib.rs:
    Matching BridgeError::DnsFailed { host, reason } DTO surfaced
    to Dart, with explicit From<CoreError::Protocol(DnsFailed)>
    mapping so the UI gets the structured fields rather than a
    stringified mess.

Tests added (crates/chanora_protocol/src/resolver.rs::tests):
  - rejects_empty
  - literal_ipv4_short_circuits
  - literal_ipv4_default_port_path
  - unresolvable_returns_dns_failed
  - resolves_known_hostname  (#[ignore], --ignored to run; hits net)

Empirical verification (2026-05-14):
  Workspace: cargo check + cargo test --workspace clean.
  Live resolver test: cn.teamspeak.app → 175.178.125.23:9987 (passes).
  cargo test -p chanora_core --test alpha_smoke -- --ignored:
    server='Vigorous Pro' channels=42 clients=20 (passes by hostname).
  flutter test: alpha_e2e_test + beta_e2e_test both green.
  Physical Moto G Stylus 5G (Android 14 arm64-v8a):
    APK rebuilt (48.9 MB). adb install + launch.
    Connect form left at default 'cn.teamspeak.app'.
    logcat shows:
      chanora_protocol: dns resolved input=cn.teamspeak.app
                                    resolved=175.178.125.23:9987
      tsclientlib: starting connection to 175.178.125.23:9987
      tsproto::resend: Connecting → Connected
      chanora_protocol: initial state snapshot received
    UI shows 'Connected to Vigorous Pro' / '42 channels • 20 online'.

This is the first item in Category A (post-Beta polish bundle).
Pause point: review before A.6 (full reconnect).

crates/chanora_protocol/src/adapter.rs

@@ -165,7 +165,32 @@ async fn connection_task(
     voice_in_tx: mpsc::Sender<InboundVoice>,
     ready_tx: oneshot::Sender<Result<(), ProtocolError>>,
 ) {
-    let mut builder = Connection::build(cfg.address.clone()).name(cfg.nickname.clone());
+    // Resolve the hostname OURSELVES using the platform resolver.
+    // tsclientlib's built-in hickory-resolver reads /etc/resolv.conf,
+    // which does not exist on Android or iOS — by side-stepping it
+    // here we get hostname connects working on every platform.
+    let addrs = match crate::resolver::resolve(&cfg.address).await {
+        Ok(a) => a,
+        Err(e) => {
+            let _ = ready_tx.send(Err(e));
+            return;
+        }
+    };
+    // Pick the first address (IPv4 preferred by the resolver's
+    // ordering). Future retry logic could fall back to subsequent
+    // addresses; one is enough for the Beta connect flow.
+    let resolved = addrs[0];
+    info!(
+        target: "chanora_protocol",
+        input = %cfg.address,
+        resolved = %resolved,
+        "dns resolved"
+    );
+
+    // Pass the resolved SocketAddr directly to tsclientlib so it
+    // skips its own resolver entirely (tsclientlib accepts
+    // SocketAddr via the From<SocketAddr> for ServerAddress impl).
+    let mut builder = Connection::build(resolved).name(cfg.nickname.clone());
 
     let identity = match cfg.identity.as_deref() {
         Some(s) => match Identity::new_from_str(s) {