[feat](trx-rs): expose WFM stereo denoise toggle in UI

Wire the StereoDenoise processor through the full stack:
- Add SetWfmDenoise command variant and RigCat trait method (trx-core)
- Add wfm_denoise field to RigFilterState with default true
- Add protocol command and bidirectional mapping (trx-protocol)
- Add rig_task command handler (trx-server)
- Implement set_wfm_denoise in SoapySdrRig backend
- Add /set_wfm_denoise API endpoint (trx-frontend-http)
- Add denoise checkbox in WFM controls with SSE sync and
  localStorage persistence

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

src/trx-client/trx-frontend/trx-frontend-http/assets/web/index.html

@@ -172,6 +172,10 @@
                       <option value="mono">Mono</option>
                     </select>
                   </label>
+                  <label class="wfm-control">
+                    <span class="wfm-control-label">Denoise</span>
+                    <input type="checkbox" id="wfm-denoise" checked />
+                  </label>
                   <div class="wfm-gain-group" id="sdr-gain-controls">
                     <label class="wfm-control">
                       <span class="wfm-control-label">RF Gain</span>