fix(ui): show error toast + guard double-tap on join; ntfy relay deploy

- main.ts: add showToast() — surfaces Rust connect errors that were
  previously swallowed silently (key for diagnosing "never joins calls")
- main.ts: connectPending flag prevents double-tap race on Join Voice
  and CallSetup auto-connect; hides button while connect is in-flight
- build-linux-docker.sh: send ntfy notification per-server after each
  relay deploy (shows host + version deployed)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/build-linux-docker.sh

@@ -186,6 +186,11 @@ tmux send-keys -t $TMUX_SESSION "cd $BINARY_DIR && ./wzp-relay \$RELAY_ARGS" Ent
 echo "Deploy done on $TARGET"
 DEPLOY
 
+    # Get the running version and notify
+    local DEPLOYED_VER
+    DEPLOYED_VER=$(ssh $DEPLOY_OPTS "$TARGET" "$BINARY_DIR/wzp-relay --version 2>/dev/null | awk '{print \$2}'" || echo "unknown")
+    curl -s -d "wzp-relay deployed to ${TARGET%%:*} — version $DEPLOYED_VER" "$NTFY_TOPIC" > /dev/null 2>&1 || true
+
     log "Deployed to $TARGET"
 }