feat(reflect): QUIC-native NAT reflection ("STUN for QUIC") — Phase 1

Lets a client ask its registered relay "what IP:port do you see for
me?" over the existing TLS-authenticated signal channel, returning
the client's server-reflexive address as a SocketAddr. Replaces the
need for a classic STUN deployment and becomes the bootstrap step
for future P2P hole-punching: once both peers know their own reflex
addrs, they can advertise them in DirectCallOffer and attempt a
direct QUIC handshake to each other.

Wire protocol (wzp-proto):
- SignalMessage::Reflect — unit variant, client -> relay
- SignalMessage::ReflectResponse { observed_addr: String } — relay -> client
- JSON-serde, appended at end of enum: zero ordinal concerns,
  backward compat with pre-Phase-1 relays by construction (older
  relays log "unexpected message" and drop; newer clients time out
  cleanly within 1s).

Relay handler (wzp-relay/src/main.rs, signal loop):
- New match arm next to Ping reuses the already-bound `addr` from
  connection.remote_address() and replies with observed_addr as a
  string. debug!-level log on success, warn!-level on send failure.

Client side (desktop/src-tauri/src/lib.rs):
- SignalState gains pending_reflect: Option<oneshot::Sender<SocketAddr>>.
- get_reflected_address Tauri command installs the oneshot before
  sending Reflect and awaits it with a 1s timeout; cleans up on
  every exit path (send failure, timeout, parse error).
- recv loop's new ReflectResponse arm fires the pending sender or
  emits a debug log for unsolicited responses — never crashes the
  loop on malformed input.
- Integrated into invoke_handler! alongside the other signal
  commands.

UI (desktop/index.html + src/main.ts):
- New "Network" section in settings panel with a "Detect" button
  that displays the reflected address or a categorized warning
  ("register first" / "relay does not support reflection" / error).

Tests (crates/wzp-relay/tests/reflect.rs — 3 new, all passing):
- reflect_happy_path: client on loopback gets back 127.0.0.1:<its own port>
- reflect_two_clients_distinct_ports: two concurrent clients see
  their own distinct ports, proving per-connection remote_address
- reflect_old_relay_times_out: mock relay that ignores Reflect —
  client times out between 1000-1200ms and does not hang

Also pre-existing test bit-rot unrelated to this PR — fixed so the
full workspace `cargo test` goes green:
- handshake_integration tests in wzp-client, wzp-relay and
  featherchat_compat in wzp-crypto all missed the `alias` field
  addition to CallOffer and the 3-arg form of perform_handshake
  plus 4-tuple return of accept_handshake. Updated to the current
  API surface.

Results:
  cargo test --workspace --exclude wzp-android: 386 passed
  cargo check --workspace: clean
  cargo clippy: no new warnings in touched files

Verification excludes wzp-android because it's dead code on this
branch (Tauri mobile uses wzp-native instead) and can't link -llog
on macOS host — unchanged status quo.

PRD: .taskmaster/docs/prd_reflect_over_quic.txt
Tasks: 39-46 all completed

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

desktop/src/main.ts

@@ -83,6 +83,8 @@ const sRoom = document.getElementById("s-room") as HTMLInputElement;
 const sAlias = document.getElementById("s-alias") as HTMLInputElement;
 const sOsAec = document.getElementById("s-os-aec") as HTMLInputElement;
 const sDredDebug = document.getElementById("s-dred-debug") as HTMLInputElement;
+const sReflectedAddr = document.getElementById("s-reflected-addr") as HTMLSpanElement;
+const sReflectBtn = document.getElementById("s-reflect-btn") as HTMLButtonElement;
 const sAgc = document.getElementById("s-agc") as HTMLInputElement;
 const sQuality = document.getElementById("s-quality") as HTMLInputElement;
 const sQualityLabel = document.getElementById("s-quality-label")!;
@@ -757,6 +759,36 @@ function renderSettingsRecentRooms(rooms: RecentRoom[]) {
 
 settingsBtnHome.addEventListener("click", openSettings);
 settingsBtnCall.addEventListener("click", openSettings);
+// "STUN for QUIC" — ask the registered relay for our own public
+// address. Requires register_signal to have been run first
+// (otherwise the Rust side returns "not registered"). The button
+// shows its working state inline so the user knows it's waiting on
+// the relay rather than the network.
+sReflectBtn.addEventListener("click", async () => {
+  sReflectedAddr.textContent = "querying...";
+  sReflectBtn.disabled = true;
+  try {
+    const addr = await invoke<string>("get_reflected_address");
+    sReflectedAddr.textContent = addr;
+    sReflectedAddr.style.color = "var(--green)";
+  } catch (e: any) {
+    // Two main failure modes surfaced via the error string:
+    //  - "not registered"                 — user hasn't registered
+    //                                        against a relay yet
+    //  - "reflect timeout (relay may not support reflection)"
+    //                                       — old relay, pre-Phase-1
+    const msg = String(e);
+    sReflectedAddr.textContent = msg.includes("not registered")
+      ? "⚠ register first"
+      : msg.includes("timeout")
+      ? "⚠ relay does not support reflection"
+      : `⚠ ${msg}`;
+    sReflectedAddr.style.color = "var(--yellow)";
+  } finally {
+    sReflectBtn.disabled = false;
+  }
+});
+
 settingsClose.addEventListener("click", closeSettings);
 settingsPanel.addEventListener("click", (e) => { if (e.target === settingsPanel) closeSettings(); });