Fix MQTT implementation, align with DStarGateway, and add documentation

[MW0MWZ]

Summary

This fixes and completes the existing MQTT support in ircDDBGateway, aligning it with the conventions established in DStarGateway and MMDVMHost. It also adds comprehensive documentation and example configuration files.

This is the first pass at these improvements; there may be follow-up commits required once validated on live hardware.

What's included

• MQTT shutdown safety — added mosquitto_loop_stop() before mosquitto_destroy() to prevent a background thread zombie/use-after-free on exit, and MQTTLogFinalise() calls in both daemon and GUI shutdown paths to ensure clean disconnection
• DStarGateway JSON compatibility — link status JSON events now use the same field names as DStarGateway (repeater, reflector, protocol, reason, action) so the same dashboard code works for both gateways
• MQTT authentication — added mqttAuth, mqttUsername, mqttPassword config keys for broker authentication
• Configurable client name — added mqttName config key, used as both the MQTT client name and topic prefix
• PID-based client IDs — avoids the time_t truncation issue on 32-bit ARM (same fix as DStarGateway/MMDVMHost)
• std::string MQTT interface — no wxString in the MQTT layer, cleaner separation of concerns
• Config parser bug fix — added empty-line crash guard (str.IsEmpty() check before GetChar()) in IRCDDBGatewayConfig, TimerControlConfig, and TimeServerConfig parsers
• Documentation — MQTT.md (config, topic structure, JSON examples, troubleshooting), CONFIGURATION.md (full reference for every config setting across all programs), BUILD.md (build parameters and dependencies), modernised README.md with feature list and DStarGateway recommendation
• Example configs — linux/ircddbgateway.example, linux/timeserver.example, linux/timercontrol.example with correct defaults

MQTT is always compiled in

Unlike DStarRepeater (which uses make MQTT=1), ircDDBGateway's Makefile unconditionally links -lmosquitto. MQTT code is always present in the binary. To disable MQTT at runtime, leave mqttAddress empty in the config file.

JSON link events

All ~30 WriteJSON call sites across DPlus, DExtra, DCS, and CCS protocol handlers have been updated to use the new DStarGateway-compatible signatures:

{"link":{"timestamp":"2025-03-08T14:23:15Z","repeater":"GB7XX  B","action":"linking","reason":"network","reflector":"REF001 C","protocol":"dextra"}}

Files changed

Area	Files
MQTT connection + shutdown fix	Common/MQTTConnection.cpp, Common/MQTTConnection.h
MQTT log + JSON events	Common/MQTTLog.cpp, Common/MQTTLog.h
Config parsing + MQTT keys	Common/IRCDDBGatewayConfig.cpp, Common/IRCDDBGatewayConfig.h
JSON event call sites	Common/CCSHandler.cpp, Common/DCSHandler.cpp, Common/DExtraHandler.cpp, Common/DPlusHandler.cpp
App lifecycle (shutdown cleanup)	ircDDBGateway/IRCDDBGatewayApp.cpp, ircDDBGateway/IRCDDBGatewayAppD.cpp
Status delegation	ircDDBGateway/IRCDDBGatewayThread.cpp
Config parser bug fix	TimeServer/TimeServerConfig.cpp, TimerControl/TimerControlConfig.cpp
Documentation	README.md, BUILD.md, MQTT.md, CONFIGURATION.md
Example configs	linux/ircddbgateway.example, linux/timeserver.example, linux/timercontrol.example