feat: activate BunkerM MQTT broker + fix Telegraf

- BunkerM: recreated with port 1883 (external) -> 1900 (internal)
- BunkerM: disabled dynsec plugin, using password_file auth (bunker/bunker)
- Simulator: ENABLE_BUNKER=1, BUNKERM_PORT=1900
- Telegraf: reactivated BunkerM consumer on port 1900
- Telegraf: recreated container (3 MQTT consumers connected)
- Grafana: dashboard v4 with corrected Flux queries
- Grafana: datasource fixed (bucket=smartcity, token=my-super-token)

Verified:
- Simulator publishes to EMQX ✅, Mosquitto ✅, BunkerM ✅
- Telegraf receives from all 3 brokers ✅
- InfluxDB has data from all brokers ✅
- Grafana dashboard displays data ✅

scripts/bunkerm-init.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+# BunkerM init script - create MQTT user and start services
+set -e
+
+# Create MQTT user if password file is empty or doesn't exist
+if [ ! -s /etc/mosquitto/mosquitto_passwd ]; then
+    echo "Creating bunker MQTT user..."
+    mosquitto_passwd -b /etc/mosquitto/mosquitto_passwd bunker bunker 2>/dev/null || true
+    chown root:root /etc/mosquitto/mosquitto_passwd 2>/dev/null || true
+    chmod 0700 /etc/mosquitto/mosquitto_passwd 2>/dev/null || true
+fi
+
+# Execute the original entrypoint
+exec /bin/sh -c '/docker-entrypoint.sh'