style: small panel polish

Energy unit moves from spinbox suffix to the label (the suffix ate
field width next to the new spin arrows); samcam exposure/gain get a
3:2 stretch so 3-decimal exposure isn't cut; the Exp. Config. tab bar
gets a BANNER_TAB_GAP spacer under its banner.

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

src/aare/gui/panels/data_collection_settings.py

@@ -20,6 +20,7 @@ from aare.gui.panels.raster_data_collection import RasterDataCollectionPanel
 from aare.gui.panels.rotation_data_collection import RotationDataCollectionPanel
 from aare.gui.panels.smart_rotation_panel import SimpleRotationSettingsPanel
 from aare.gui.scan_logic.raster_grid_manager import RasterGridManager
+from aare.gui.styles import BANNER_TAB_GAP
 from aare.gui.widgets.title_label import TitleLabel, tighten_column
 
 
@@ -102,6 +103,9 @@ class DataCollectionSettings(QFrame):
                 "Experiment configuration", exp_config, collapsible=True, default_collapsed=False
             )
         )
+        # Explicit spacer, not layout spacing: the tab bar must keep sitting
+        # flush on the pane below, only the banner gets breathing room.
+        exp_config_layout.addSpacing(BANNER_TAB_GAP)
         exp_config_layout.addWidget(self._tab_bar)
         exp_config_layout.addWidget(pane)
         v_layout.addWidget(exp_config)

src/aare/gui/panels/monochromator_panel.py

@@ -23,13 +23,14 @@ class MonochromatorPanel(QWidget):
 
         # One row (label | value | button) instead of three — vertical space.
         # Display in keV; the DAQ API stays in eV (converted on emit).
-        grid_layout.addWidget(QLabel("Energy", parent=self), 2, 0)
+        # Unit lives in the label, not as a spinbox suffix — the suffix ate
+        # field width and sat between the value and the +/- arrow.
+        grid_layout.addWidget(QLabel("Energy (keV)", parent=self), 2, 0)
 
         self.energy_spin = QDoubleSpinBox(parent=self)
         self.energy_spin.setDecimals(3)
         self.energy_spin.setRange(1.0, 30.0)
         self.energy_spin.setSingleStep(0.1)
-        self.energy_spin.setSuffix(" keV")
         self.energy_spin.setValue(12.0)
         grid_layout.addWidget(self.energy_spin, 2, 1)
 

src/aare/gui/panels/samcam_panel.py

@@ -54,10 +54,12 @@ class SamcamPanel(QWidget):
         self.gain_spinbox.setDecimals(1)
         self.gain_spinbox.valueChanged.connect(self._changed)
 
+        # 3:2 stretch — exposure shows 3 decimals plus the side arrows and
+        # was getting cut; gain (1 decimal) can afford the narrower field.
         exposure_gain_layout.addWidget(QLabel("Exposure (s):"))
-        exposure_gain_layout.addWidget(self.exposure_spinbox)
+        exposure_gain_layout.addWidget(self.exposure_spinbox, 3)
         exposure_gain_layout.addWidget(QLabel("Gain:"))
-        exposure_gain_layout.addWidget(self.gain_spinbox)
+        exposure_gain_layout.addWidget(self.gain_spinbox, 2)
 
         # Persist the current gain/exposure as the beam-location preset for the
         # current zoom (only meaningful in beam-location mode).

src/aare/gui/styles.py

@@ -93,6 +93,11 @@ FRAME_L3_COLOR = "#c9cfd8"
 # left edge lines up with the left-column panels above (Loop centering).
 DOCK_CONTENT_LEFT_PAD = 10
 
+# Gap (px, int — used in code, not QSS) between a TitleLabel banner and a tab
+# bar sitting directly under it (Exp. Config.), so the tabs don't touch the
+# banner's bottom edge line.
+BANNER_TAB_GAP = 6
+
 # Resize-line hint: dock separators stay invisible until the mouse rests on
 # one for SEPARATOR_HINT_DELAY_MS (or a drag starts) — then only the exact
 # separator under the cursor fills with SEPARATOR_HINT. The rest/drag gate