Radio onboarding: guided setup for a radio with no region #7940

Add a guided setup for a connected radio per the design spec: meshtastic/design#175 (items 4 to 15).

• Open it on its own, once per radio, when the radio's region is known and is UNSET. Keep it reachable from Connect and from radio settings afterwards. Write only to the connected radio.
• Pages: intro, region, preset, name, then a summary. Licensed operators skip the name page.
• Region list leaves out regions the firmware can't use; a suggested region is only a starting point the user confirms.
• On 2.8, the preset list follows the radio's region preset map, and a factory-fresh US radio on Long Fast moves to Long Turbo. Custom modem settings survive a region change.
• One LoRa config write, only on a change. Warn about the restart below 2.8; on 2.8 ask for the node database again.
• On 2.8, an optional status message with the names, and a Nearby Meshes page: Listen for Beacons, beacons heard so far with Join and Add, and links to discovery and the beacon settings.

This would replace the Set your region card's job of sending people to the LoRa screen. The first-launch welcome and permission pages already match items 1 to 3.

Prior art: meshtastic/Meshtastic-Apple#2873 and meshtastic/Meshtastic-Apple#2906. Spec: specs/021-onboarding-radio-setup/spec.md in Meshtastic-Apple.

See design#175 for the full rules and open questions.