feat: current energy readout in Exp. Config energy row

Mirrors the Beamline setup live readout above Set Energy, fed by the
same DAQ tick with the zero-energy guard and repaint skip.

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

src/aare/gui/panels/data_collection_settings.py

@@ -85,6 +85,17 @@ class DataCollectionSettings(QFrame):
         centering_layout.addWidget(self.find_tip)
         centering_layout.addWidget(self.bounding_box)
 
+        # Live readout mirrored from the Beamline setup panel, same reason:
+        # "what is" and "what to set" must not share one ambiguous row.
+        # Fed per DAQ tick in update_daq_status.
+        self.current_energy_label = QLabel("—", parent=self)
+        current_energy_row = QWidget(self)
+        current_energy_layout = QHBoxLayout(current_energy_row)
+        current_energy_layout.setContentsMargins(0, 0, 0, 0)
+        current_energy_layout.addWidget(QLabel("Current energy / λ", parent=current_energy_row))
+        current_energy_layout.addWidget(self.current_energy_label)
+        current_energy_layout.addStretch()
+
         # Energy row copied from the Beamline setup panel so users can change
         # energy without leaving the experiment configuration.
         self.energy_spin = QDoubleSpinBox(parent=self)
@@ -110,6 +121,7 @@ class DataCollectionSettings(QFrame):
         # border, and the Abort button should hug the pane.
         pane_layout.setContentsMargins(6, 6, 6, 0)
         pane_layout.addWidget(centering_row)
+        pane_layout.addWidget(current_energy_row)
         pane_layout.addWidget(energy_row)
         pane_layout.addWidget(self._stack)
 
@@ -182,6 +194,17 @@ class DataCollectionSettings(QFrame):
 
     @Slot(DAQStatusModel)
     def update_daq_status(self, s: DAQStatusModel):
+        energy = s.diffraction.energy_keV
+        # 0.0 is the server's detector-unavailable fallback, and the
+        # wavelength property divides by it — guard before touching it.
+        if not energy:
+            text = "— / —"
+        else:
+            text = f"{energy:.3f} keV  /  {s.diffraction.wavelength_angstrom:.4f} Å"
+        # Guarded: runs per DAQ tick (2 Hz), skip the repaint when unchanged.
+        if self.current_energy_label.text() != text:
+            self.current_energy_label.setText(text)
+
         self.raster.update_daq_status(s)
         self.screening.update_daq_status(s)
         self.simple.update_daq_status(s)