Add MQTT support for real-time communication alongside existing HTTP API

[Copilot]

This PR implements MQTT communication support while maintaining 100% backward compatibility with the existing HTTP API. The integration follows the requirement to "keep the models as close as they currently are" by wrapping existing models in MQTT-specific containers without modifying the original model definitions.

Key Features

✅ Zero Breaking Changes

• All existing models (Person, Plant, Sensor, SensorResult) remain completely unchanged
• HTTP API works identically to before
• Default behavior is HTTP-only mode (no MQTT dependency required)

✅ MQTT Integration

• Eclipse Paho MQTT v5 Client - Industry standard, reliable MQTT library for Scala
• Environment-configurable - Enable with MQTT_ENABLED=true
• Structured topic hierarchy for different entity types and real-time data
• JSON serialization/deserialization for all model types
• Graceful connection management with automatic reconnection

✅ Real-time Capabilities

• Entity creation events published to topics like leaf-lab/person/created
• Live sensor readings on leaf-lab/plant/{plant_id}/sensor/{sensor_id}/reading
• Bidirectional communication - can receive MQTT messages and store to database

Usage Examples

HTTP-only (unchanged default):

sbt run

HTTP + MQTT:

MQTT_ENABLED=true MQTT_BROKER_URL=tcp://localhost:1883 sbt run

MQTT Message Format:

{
  "sensorResult": {
    "id": 1,
    "plant_id": 1,
    "sensor_id": 1,
    "value": "25.5",
    "as_of": "2025-06-03T00:26:17.617168388Z"
  },
  "messageId": "uuid-string"
}

Architecture

The implementation adds MQTT as a parallel communication channel:

HTTP Requests ──┐
                ├──► Service Layer ──► Repository Layer ──► Database
MQTT Messages ──┘                 └──► MQTT Publisher

• MqttModels.scala - Wrapper classes that preserve original model structure
• MqttService.scala - MQTT client management and message handling
• MqttEnabledService.scala - Enhanced service that publishes to MQTT on entity creation
• MqttConfig.scala - Environment-based configuration

Testing

# Test MQTT model serialization
sbt "runMain dev.whalenet.leaf_lab.MqttTest"

# Compile verification
sbt clean compile

All tests pass and demonstrate proper JSON serialization, topic generation, and model preservation.

Repository Impact

• Files added: 6 new MQTT-specific files + documentation
• Files modified: build.sbt (1 dependency), Main.scala (MQTT initialization)
• Files unchanged: Models.scala, Service.scala, Repository.scala, Database.scala
• Backward compatibility: 100% - existing HTTP workflows unaffected

This implementation provides a foundation for transitioning to MQTT while maintaining all current functionality and allowing gradual migration.

Fixes #18.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• esm.ubuntu.com
  • Triggering command: /usr/lib/apt/methods/https (dns block)
• git.io
  • Triggering command: curl -Ls REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list

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