[PXCT-1536] Uno Q - network mode fixes

[91volt]

Summary

This PR improves the Arduino UNO Q User Manual by clarifying how Network Mode works in Arduino App Lab.
It explains that Network Mode relies on local network discovery (mDNS) and that some network configurations may prevent automatic discovery, even when the board is connected to Wi-Fi and reachable by IP.

What This PR Changes

• Updated the Network Mode section to clarify that boards appear only when discoverable on the local network
• Added a short explanation of mDNS-based discovery and its limitations
• Clarified that IP, SSH, or browser access does not guarantee visibility in Network Mode

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