XIAO ESP32S3 multi-board MQTT dashboard

Architecture: N boards (STA mode, same WiFi) → MQTT broker (Mosquitto, one PC on that WiFi) → browser dashboard (MQTT-over-WebSocket, mqtt.js). Each board runs the same compiled firmware — no per-board edits — because it derives a unique ID from its own MAC address.

Read the xiao-esp32s3 skill (same repo) first for base arduino-cli workflow and pitfalls (PSRAM flag, DTR reset-stuck recovery, bounded serial reads). This skill adds the broker + networking + dashboard layer on top.

Step 1 — ALWAYS ask the user first

Never invent credentials or assume where the broker runs. Ask for: