Harden online menu server discovery

[IIPoliII]

Summary

• replace the online menu's Unity WWW fetch with a managed background request so HTTPS failures no longer crash the game
• enable modern TLS protocols, guard Lidgren discovery calls, and surface clear errors when the server list cannot be reached
• ignore malformed server list entries and handle discovery exceptions so the menu stays responsive on misconfigured machines

Testing

• not run (Unity project)

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https://chatgpt.com/codex/tasks/task_e_68cedcba97fc8325b37aeec72b0c4905