Add port documentation and WebUI display for Home Assistant serial connection

[Copilot]

Users attempting to connect Home Assistant's OpenTherm Gateway integration were using port 23 (telnet debug) instead of port 25238 (serial interface), resulting in connection failures. The firmware provides both ports but lacked clear documentation distinguishing their purposes.

Changes:

• README.md: Added connectivity table documenting port usage (80=HTTP, 23=Telnet, 25238=Serial) with explicit Home Assistant integration instructions
• restAPI.ino: Exposed serialtcpport field in device info API endpoint
• data/index.js: Added connection information panel to device info page displaying formatted connection strings including socket://<ip>:25238 for serial interface

Example WebUI output:

Connection Information:
• Web Interface: http://192.168.1.100
• Telnet (Debug): telnet 192.168.1.100 23
• Serial (OTmonitor/HA): socket://192.168.1.100:25238

For Home Assistant OpenTherm Gateway integration, use the Serial connection string above.

The device info page now prominently displays the correct connection string eliminating port confusion.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Home Assistant OpenTherm Gateway Integration Failed to Connect</issue_title>
<issue_description>Hello,

I got an OpenTherm Gateway from nodo shop, pre-soldered and configured. I plugged it in and configured the wifi. I struggled to set up the OpenTherm Gateway integration in Home Assistant though. I used nmap to check which ports were open (80 and 23) and I set the address of the OTGW to socket://192.168.50.207:23 (the IP is static of course). It keeps telling me it failed to connect, I tried without port, without socket://. I can connect to it from the otmonitor Windows utility, and I was able to configure and use it with MQTT in Home Assistant, but I would prefer to use the OpenTherm Gateway Integration. I am not sure how to get it working though...

Log entry:

Logger: pyotgw.connection
Source: runner.py:289
First occurred: 1:31:11 PM (2 occurrences)
Last logged: 1:32:07 PM

The serial device on socket://192.168.50.207:23 is not responding. Will keep trying.

HA Info:

Installation method
Home Assistant OS
Core 2025.11.2
Supervisor 2025.11.2
Operating System 16.3
Frontend 20251105.0

OTGW firmware:

Firmware name Version Size
diagnose.hex 2.1 9196
gateway.hex 6.6 26996
interface.hex 2.0 10488
</issue_description>

Comments on the Issue (you are @copilot in this section)

@rvdbreemen Also you seem to use the home assistant serial port integration. There might be errors in the log. I have never used that integration not sure why it's giving errors now.

But the MQTT auto discovery integration works just fine.

Hope to hear once you get it setup properly.

Robert</comment_new>

• Fixes Home Assistant OpenTherm Gateway Integration Failed to Connect #270

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