fix(mesh): native E2E DM for archy↔archy text + software radio-reboot

- send_message now sends archy↔archy plain text as a native TEXT_MESSAGE_APP
  DM (firmware PKC-encrypts E2E), not wrapped in the binary typed envelope
  that silently broke archy↔archy LoRa delivery. Archy peers' Sent rows are
  marked encrypted so the E2E pill shows; rich typed msgs still use the
  typed-wire path.
- Add a software radio-reboot to recover a wedged/RX-deaf radio without
  physical access (and for the Device-tab settings panel): driver reboot()
  via AdminMessage reboot_seconds=97 (verified vs meshtastic/protobufs),
  MeshCommand::RebootRadio, MeshService::reboot_radio, RPC mesh.reboot-radio.
- Handoff doc: docs/SESSION-1.8.0-OTA-PROGRESS.md "RESUME HERE" — RF link is
  the proven blocker (radios not hearing each other); modem_preset mismatch
  is the prime suspect; on-device Meshtastic-app check + fix plan documented.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

core/archipelago/src/api/rpc/dispatcher.rs

@@ -366,6 +366,7 @@ impl RpcHandler {
             "mesh.send" => self.handle_mesh_send(params).await,
             "mesh.send-channel" => self.handle_mesh_send_channel(params).await,
             "mesh.broadcast" => self.handle_mesh_broadcast().await,
+            "mesh.reboot-radio" => self.handle_mesh_reboot_radio(params).await,
             "mesh.configure" => self.handle_mesh_configure(params).await,
             "mesh.send-invoice" => self.handle_mesh_send_invoice(params).await,
             "mesh.send-coordinate" => self.handle_mesh_send_coordinate(params).await,