Toggling 'Route via WSS' (or any stealth option) only wrote the
setting: sessions read stealth options exclusively in refreshOptions()
during (re)connect, so the change stayed inert until something else
restarted MTP - which is why WSS only started working after flipping
the IPv6 checkbox, the one control that called mtp().restart().
Application::applyProxyStealthOptions() now writes the setting,
schedules a settings save and restarts every account's connections
through the existing proxyChanges() pipeline, debounced by 1.5s so
typing in the custom WSS relay fields does not restart per keystroke.
All nine stealth setters in the proxy box go through it.
setTryIPv6 also switches from restarting only the active account's
instance to restartProxyConnections(), covering multi-account setups.
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