fix(runtime): harden mobile QR smoke output (#2417)

Harvested from #2415 with thanks to @axobase001.

Keeps the denser mobile QR renderer and replaces the fixed binding-warning sleep with health polling plus an explicit timeout failure path, so slow starts fail with the useful cause instead of drifting into misleading assertions.

Follow-up to #2403.

scripts/mobile-smoke.sh

@@ -155,7 +155,20 @@ log "=== Test Group 3: Binding warnings (0.0.0.0 default) ==="
 STDOUT_FILE=$(mktemp)
 "$BINARY" serve --port "$PORT" --mobile --insecure > "$STDOUT_FILE" 2>&1 &
 SERVER_PID=$!
-sleep 2
+SERVER_READY=0
+for _ in $(seq 1 30); do
+    if curl -sf "http://127.0.0.1:${PORT}/health" > /dev/null 2>&1; then
+        SERVER_READY=1
+        break
+    fi
+    sleep 0.3
+done
+if [[ "$SERVER_READY" -ne 1 ]]; then
+    rm -f "$STDOUT_FILE"
+    fail "Server did not become ready on port $PORT"
+    cleanup
+    exit 1
+fi
 STDOUT=$(cat "$STDOUT_FILE")
 rm -f "$STDOUT_FILE"