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/api/rpc/mesh/messaging.rs

@@ -158,6 +158,29 @@ impl RpcHandler {
                 anyhow::bail!("Unknown LoRa region: {trimmed}");
             }
         }
+        // Meshcore LoRa PHY params (freq/bw/sf/cr, firmware field units — see
+        // mesh::LoraRadioParams). Validated against the firmware's accepted
+        // ranges here so a bad value errors at the API instead of being sent
+        // to the radio and rejected on-device. `null` clears the setting.
+        if let Some(rp) = params.get("lora_radio_params") {
+            if rp.is_null() {
+                config.lora_radio_params = None;
+            } else {
+                let parsed: mesh::LoraRadioParams = serde_json::from_value(rp.clone())
+                    .map_err(|e| anyhow::anyhow!("Invalid lora_radio_params: {e}"))?;
+                anyhow::ensure!(
+                    (150_000..=2_500_000).contains(&parsed.freq_khz),
+                    "freq_khz out of range (150000..=2500000)"
+                );
+                anyhow::ensure!(
+                    (7_000..=500_000).contains(&parsed.bw_hz),
+                    "bw_hz out of range (7000..=500000)"
+                );
+                anyhow::ensure!((5..=12).contains(&parsed.sf), "sf out of range (5..=12)");
+                anyhow::ensure!((5..=8).contains(&parsed.cr), "cr out of range (5..=8)");
+                config.lora_radio_params = Some(parsed);
+            }
+        }
         // Firmware pin: probe only the named firmware on the port ("auto"/""
         // clears the pin and restores strict-probe auto-detect).
         if let Some(kind) = params.get("device_kind").and_then(|v| v.as_str()) {