feat(mesh): operator-configurable Meshcore LoRa PHY params (freq/bw/sf/cr)

Archy set no radio params on Meshcore devices — SF/CR/BW/freq lived only in
device firmware, so a radio on the wrong preset could not be fixed from the
node (it hears RF energy but demodulates nothing; the fleet hit exactly this
on an RNode: docs/RETICULUM-TRANSPORT-PROGRESS.md item 4).

- protocol.rs: build_set_radio_params — wire format verified against the
  MeshCore companion firmware handler (CMD_SET_RADIO_PARAMS=11:
  [11][freq:u32 LE MHz*1000][bw:u32 LE kHz*1000][sf][cr]); byte-layout test
  pinned to the Portugal preset 869.618 MHz / 62.5 kHz / SF8 / CR8.
- serial.rs: MeshcoreDevice::set_radio_params (device reboots on OK).
- MeshConfig.lora_radio_params: Option — None (default) leaves the radio
  untouched, so only explicitly-configured deployments are affected.
- session.rs: provision on connect, gated on a persisted last-applied marker
  (SELF_INFO offsets shift across firmware versions) + the same attempt cap
  as region/channel so a refusing radio never reboot-loops.
- mesh.configure RPC: lora_radio_params arm with firmware-range validation.

mesh tests: 114/114 pass.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/archipelago/src/mesh/serial.rs

@@ -164,6 +164,29 @@ impl MeshcoreDevice {
         Ok(())
     }
 
+    /// Set the radio's LoRa PHY parameters (freq/bw/sf/cr, firmware field
+    /// units — see `protocol::build_set_radio_params`). On RESP_OK the
+    /// firmware persists the params and reboots to apply them, so the caller
+    /// must treat the session as gone and reconnect.
+    pub async fn set_radio_params(
+        &mut self,
+        freq_khz: u32,
+        bw_hz: u32,
+        sf: u8,
+        cr: u8,
+    ) -> Result<()> {
+        self.send_raw(&protocol::build_set_radio_params(freq_khz, bw_hz, sf, cr))
+            .await?;
+        let frame = self.recv_frame_timeout(READ_TIMEOUT).await?;
+        if frame.code == protocol::RESP_ERR {
+            anyhow::bail!(
+                "Set radio params failed: {}",
+                protocol::parse_error(&frame.data)
+            );
+        }
+        Ok(())
+    }
+
     /// Broadcast our advertisement to the mesh.
     pub async fn send_self_advert(&mut self) -> Result<()> {
         self.send_raw(&protocol::build_send_self_advert()).await?;