feat(trx-core,trx-protocol,trx-backend-soapysdr): add spectrum data pipeline

Add SpectrumData struct (bins, center_hz, sample_rate) to RigState and
RigSnapshot. Add GetSpectrum RigCommand and ClientCommand plumbed through
the protocol layer. SoapySDR DSP pipeline now computes a 1024-bin FFT
(Hann window, FFT-shifted, dBFS) every 4 IQ blocks (~10 Hz update rate)
and exposes it via RigCat::get_spectrum(). The rig_task handles
GetSpectrum without persisting spectrum data in ongoing state.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-protocol/src/codec.rs

@@ -403,6 +403,7 @@ mod tests {
             cw_wpm: 0,
             cw_tone_hz: 0,
             filter: None,
+            spectrum: None,
         }
     }
 }

src/trx-protocol/src/mapping.rs

@@ -47,6 +47,7 @@ pub fn client_command_to_rig(cmd: ClientCommand) -> RigCommand {
         ClientCommand::ResetWsprDecoder => RigCommand::ResetWsprDecoder,
         ClientCommand::SetBandwidth { bandwidth_hz } => RigCommand::SetBandwidth(bandwidth_hz),
         ClientCommand::SetFirTaps { taps } => RigCommand::SetFirTaps(taps),
+        ClientCommand::GetSpectrum => RigCommand::GetSpectrum,
     }
 }
 
@@ -86,6 +87,7 @@ pub fn rig_command_to_client(cmd: RigCommand) -> ClientCommand {
         RigCommand::ResetWsprDecoder => ClientCommand::ResetWsprDecoder,
         RigCommand::SetBandwidth(bandwidth_hz) => ClientCommand::SetBandwidth { bandwidth_hz },
         RigCommand::SetFirTaps(taps) => ClientCommand::SetFirTaps { taps },
+        RigCommand::GetSpectrum => ClientCommand::GetSpectrum,
     }
 }
 

src/trx-protocol/src/types.rs

@@ -37,6 +37,7 @@ pub enum ClientCommand {
     ResetWsprDecoder,
     SetBandwidth { bandwidth_hz: u32 },
     SetFirTaps { taps: u32 },
+    GetSpectrum,
 }
 
 /// Envelope for client commands with optional authentication token and rig routing.