Avoid restart warning for hostname-only network changes

[0xjc65eth]

Summary

• only show the network restart warning when Wi-Fi settings changed
• keep hostname-only saves quiet because the hostname is reflected without a restart
• only enable the Restart button after saves that actually need a restart

Fixes #581

Testing

• git diff --check
• npm run build

Note: the frontend build still reports the existing initial bundle budget warning.

[0xjc65eth]

Closing this for now to reduce maintainer review load, per feedback from @mutatrum. I am keeping #1705 open as the single focused PR because it is small, UI-only, and already has an ack. Happy to revisit this later only if maintainers ask for it. Thanks for the feedback and for maintaining the project.