MQTT must be dynamic port

[Pushkinmazila2]

Title: MQTT transport uses hardcoded port 1883 instead of configurable endpoint

Description:

Currently MQTT transport initializes connections with a hardcoded port:

MqttOptions::new(client_id, server_uri, 1883);

Additionally, port 1883 appears across multiple modules:

• transport/mqtt.rs
• flow_j_mqtt.rs
• peer_registry.rs
• tests

This prevents:

• using MQTT over TLS (port 8883)
• running over WebSockets (common in restrictive networks)
• proper stealth configuration (e.g., port 443)

Expected behavior:

• Parse port from server_uri or config
• Support TLS (8883) and custom ports
• Allow fallback to HTTPS-like ports for evasion

Suggestion:
Introduce a unified broker parser:

host:port → (host, port)

and pass port dynamically into MqttOptions.

Impact:
This is critical for real-world deployment and contradicts the "stealth" goals described in README.