CUB-231: Mosquitto MQTT broker setup on Pi Zero 2 W hub

- Install script for Mosquitto MQTT broker on Pi Zero 2 W (10.60.1.101)
- Persistence enabled with data stored in /var/lib/mosquitto/data/
- Topic ACL configuration for hub, sensor, mobile, and admin users
- systemd service with security hardening (NoNewPrivileges, ProtectSystem)
- Configuration files: mosquitto.conf, acl.conf
- Validation script to verify setup before deployment

acl.conf

@@ -0,0 +1,20 @@
+# Access Control List for Mosquitto
+# Topic patterns with user permissions
+
+# Hub - Internal services (full access)
+user hub
+topic # rw
+
+# Sensors - Read sensor data, write commands
+user sensor
+pattern read sensors/+/data
+pattern write devices/+/commands
+
+# Mobile - Home status and control
+user mobile
+pattern read home/+/status
+pattern write home/+/control
+
+# Admin - Full access to all topics
+user admin
+topic # rw