Persist nickname and server list validation updates

[IIPoliII]

Summary

• ensure nicknames are trimmed, fall back to a default value, and are saved immediately through a reusable helper
• reuse the new helper when applying options so updated settings are persisted even if the game closes unexpectedly
• keep the options UI resilient to missing nickname data when refreshing fields

Testing

• not run (Unity editor not available in container)

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https://chatgpt.com/codex/tasks/task_e_68ceceab0c2c8325bc658f6d7f654ce9