Firmware, investigate MQTT setup behavior and report LittleFS page version

[nk25719]

Description

The MQTT setup workflow is showing inconsistent or unexpected behavior.

Add a way to identify the version of the web pages installed in LittleFS.

Tasks

• Reproduce and corner the MQTT setup issue.
• Check configuration saving, reconnection, and reboot behavior.
• Add a version identifier for the LittleFS pages. Display the LittleFS version in the UI or through a diagnostic endpoint.

Acceptance criteria

• MQTT settings save and reload correctly.
• The installed LittleFS page version can be identified.