feat(settings): connection toggles in Downloads & Sharing + mdns i18n

[lukyrys]

Three small changes in the same logical area — Settings → Downloads & Sharing.

What changes

• New toggle useRelayClients (default ON) between maxRelayReservations and maxRelayClients. When OFF, the node no longer reserves slots on foreign relays (discoverRelays: 0, no /p2p-circuit listen slots).
• New toggle autoConnectNewNetworks (default ON). When ON, networks added via lishnets.add and lishnets.addIfNotExists are immediately enabled=true and a lishnets:joined broadcast is emitted — the user no longer has to click a follow-up button.
• CZ + EN translations for mdnsEnabled and mdnsInterval — these last two settings rows previously rendered as raw keys.

Commits

Type	Subject
fix(i18n)	add cs/en strings for mdns settings keys
feat(settings)	add useRelayClients toggle for circuit-relay client role
feat(lishnets)	auto-enable newly added networks per autoConnectNewNetworks setting

Backwards compatibility

Both new settings default to `true` and tolerate absence in older `settings.json` (`?? true` in the frontend, `!== false` in the backend). DB schema unchanged, existing relays/networks untouched.